Marginal bone loss associated with unilateral free end mandibular implant supporting superstructures constructed with different occlusal schemes

Sara Tamimi; Mona H Mandour

doi:10.4103/tdj.tdj_71_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 20 | Issue : 2 | Page : 84-88

Marginal bone loss associated with unilateral free end mandibular implant supporting superstructures constructed with different occlusal schemes

Sara Tamimi PHD , Mona H Mandour
Department of Crowns and Bridges, Faculty of Dental Medicine for Girls, Al-Azhar University, Cairo, Egypt

Date of Submission	30-Dec-2022
Date of Decision	13-Feb-2023
Date of Acceptance	20-Feb-2023
Date of Web Publication	11-May-2023

Correspondence Address:
Sara Tamimi
Lecturer of Crowns and Bridges, Faculty of Dental Medicine for Girls, Al-Azhar University, Cairo
Egypt

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/tdj.tdj_71_22

Abstract

Aims
This study was designed to evaluate the amount of bone resorption related to implant in free end saddle in response to different occlusal designs.
Patients and methods
Twenty patients with unilateral free end saddle in the lower arch till the second premolar were selected and received delayed single dental implants replacing the first molar tooth. They were divided into two main groups according to the implant superstructure deign (n = 10). Group 1: implant-supported fixed dental prosthesis which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown smaller than the occlusal contact area of adjacent tooth. Group 2: implant-supported fixed dental prosthesis which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown larger than the occlusal contact area of adjacent tooth. Patients were evaluated for the amount of marginal bone level at the time of crown insertion, after 3 and 6 months of function.
Results
There was a statistically significant change by time in marginal bone loss in both groups especially during the first 3 months. However, there was no statistically significant difference between marginal bone loss regarding the two groups.
Conclusion
It was concluded that increasing the occlusal contact area of the implant superstructure has no effect on marginal bone loss.

Keywords: implant, occlusion, marginal bone loss, multi-layered zirconia

How to cite this article:
Tamimi S, Mandour MH. Marginal bone loss associated with unilateral free end mandibular implant supporting superstructures constructed with different occlusal schemes. Tanta Dent J 2023;20:84-8

How to cite this URL:
Tamimi S, Mandour MH. Marginal bone loss associated with unilateral free end mandibular implant supporting superstructures constructed with different occlusal schemes. Tanta Dent J [serial online] 2023 [cited 2023 May 27];20:84-8. Available from: http://www.tmj.eg.net/text.asp?2023/20/2/84/376646

Introduction

An attractive alternative to conventional restorative procedures which became available is the implant retained prostheses. Peri-implant bone level preservation is the key to implant success in long-term observation ^[1]. Several factors were reported to be associated with crestal bone loss (CBL), including bacterial colonization and the presence of a microgap between abutment and implant ^[2]. Contradictory findings on the role of occlusal overload on peri-implant bone loss have been reported, with limited evidence supporting the cause-and-effect relationship ^[3]. An excessive occlusal load on an implant-supported fixed dental prosthesis (FDP) is typically referred to as overload, and this places a lot of stress on the peri-implant bone tissue ^[4]. The likelihood of CBL may rise if there is an imbalance in the occlusal load, which could lead to stress at the bone–implant coronal first contact site ^[5]. Local, systemic, and social factors are all potential contributors to bone loss surrounding implants. Applying excessive occlusal force to implant-supported prostheses may cause peri-implantitis and perhaps lead to implant loss ^[6]. The modified occlusion used with implants is intended to lessen occlusal stresses under both axial and nonaxial loading, as well as the stresses around the implant and supporting bone structures. Additionally, it is believed that this idea of occlusal morphology contributes significantly to improving the chances of clinical survival and implant success rates ^[7]. However, the optimal occlusion for implants has not been defined due to the paucity of clinical research and the absence of results supported by data ^[8]. Occlusal loading may cause implant bone loss and/or loss of osseointegration in effectively integrated implants, according to a prior study ^[9]. An occlusal strategy called 'implant protected occlusion' is intended to increase the longevity of both the implant and the prosthetics ^[9]. Therefore, the aim of this study was to assess marginal bone loss around free-end single implant having two occlusal schemes.

Patients and methods

Sample size

Based on Thongdee et al. ^[10] and using G power statistical power analysis program (version 3.1.9.4) for sample size determination ^[11]. A total sample size n = 20 (subdivided to 10 in each group) will be sufficient to detect a large effect size (d)=1.34, with an actual power (1-β error) of 0.8 (80%) and a significance level (α error) 0.05 (5%) for two-sided hypothesis test. Therefore, the total sample size in this study was 20 patients.

Patients' grouping

Twenty patients with unilateral free end saddle till the second premolar were included in this study according to inclusion and exclusion criteria. Inclusion criteria ^[12],[13]: age from 23 to 58 years, systemically and psychologically healthy as documented by self-assessment according to the criteria of Cornell medical index ^[14], patients with missing mandibular first molar after at least 3 months of socket healing, cusp-marginal ridge occlusal arrangement, and in occlusion with natural dentition. Exclusion criteria ^[12] include inadequate bone availability, severe cranio-mandibular disorders, use of known drugs that would affect the central nervous system or neuromuscular function, severe systemic diseases or known mental disorders, periapical lesions sensitive to percussion related to the premolars adjacent to the edentulous area, anterior open occlusion, and history of parafunctional habits (clenching or bruxism). Selected patients received delayed dental implants restoring only lower first molar tooth. They were divided into two groups according to the occlusal scheme of the implant-supported prostheses. Group 1 (occlusal scheme 1); implant-supported FDP which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown smaller than the occlusal contact area of adjacent tooth. Following the principal of implant protected occlusion; the primary occlusal contact was resided opposite to the diameter of the implant within the central fossa. Marginal ridge contacts were avoided to prevent cantilever effects and bending moments. Within 1 mm of the periphery of the crown, away from the marginal ridge a secondary occlusal contact was kept to decrease moment loads. The occlusal table was designed to be narrower than the occlusal table of the mandibular first molar and the cusp inclines was decreased in height compared to mandibular first molar of the other side. Group 2 (occlusal scheme 2); implant-supported FDP which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown larger than the occlusal contact area of adjacent tooth. Patients of both groups were evaluated for the amount of marginal bone level at the time of crown insertion, after 3 and 6 month of function. A written consent was obtained from each patient after explaining the study before the initiation of any procedure, according to the guidelines of the research ethics committee in the Faculty of Dental Medicine for Girls, Al-Azhar University (REC-PD-23-2). Prior to the surgical procedure, medical evaluation was obtained, ensuring the inclusion of only medically free patients. Diagnosis was done clinically and radiographically. Preoperative periapical radiograph as well as cone-beam computed tomography scan (Soredex, Tuusula, Finland) were obtained for each patients. Clinical evaluation was done with the help of study casts and cone-beam computed tomography scan.

Surgical procedures

A full thickness flap was incised, the edges of tissues were pushed aside to expose the bone. After reflecting the flap, drilling the bone was done at a regular speed to avoid bone necrosis and enlarged gradually by using successively wider drills. The implant (Dentium Co. Ltd, Korea) was placed with a torque controlled wrench at the exact torque. A cover screw was placed to seal the implant orifice, the gingiva was adapted around the entire implant and then the flap was closed with interrupted sutures. Postoperative periapical radiograph (Kodak DF-55 #1 ultra-speed double film. Carestream. Part #: 127–3721) was taken to check implant position and to determine changes over time. The patients were told to proceed with postoperative instructions which included cold packs, admission of antibiotics and analgesics whenever regarded essential. In addition, 0.12% chlorohexidine solution was described to be utilized two times every day for 7 days. Three to six months of integrating time was allowed before fabrication of the crowns.

Impression technique

First, the healing abutments were removed, then the implant level impression transfers were screwed to the implants in the patient^'s mouth. The trays were perforated in the regions where the implants were placed to provide access for the transfer copings. Impressions (LASCOD Spa, Via Longo, 18-50019 Sesto Fiorentino, Florence, Italy) were taken for both the implant and the opposing upper arch. Implant analogs were screwed into the implant level impression transfers.

Laboratory procedures

To obtain a three-dimensional image for each case, three-dimensional optical impressions were taken by scanning the casts. A digital impression was captured for the cast with implant abutment. The articulator with casts was fixed to the extraoral three-dimensional dental scanner (Smart optics Scan Box Gmbh, Germany) to take an optical impression of the casts in occlusion.

Designing the restoration

The software calculated a virtual model from the scanned pictures. The occlusal table for each group was designed. Zirconia crowns were milled (Kurary Noritake Dental Inc., Japan), sintered, stained, and glazed. All crowns were seated on their corresponding abutments on the casts and checked for complete seating. Then, each crown was checked in the patient^'s mouth for proper marginal seal, contour, proper contact area, and proper occlusion according to each design. Articulating papers were used to determine and check the site and dimensions of the occlusal contact areas of the implant superstructure. Any occlusal contacts on the marginal ridges or cusp inclines were marked and reduced, then the crowns were reglazed.

Cementation procedure

A temporary luting cement (Dentotemp Itena, USA) was used to cement the crowns. Postcementation dental periapical radiograph was taken to detect any excess cement. Patients were evaluated for marginal bone resorption in both mesial and distal sides at the time of crown cementation, after 3 months and after 6 months follow up periods.

Standardization of the periapical radiographs

The same operator took all of the radiographs under identical circumstances using a parallel technique. The radiographs were all digitalized by a scanner and synchronised using AutoCAD software, which allowed for the modification of the few variations resulting from the radiography tube angle adjustment. Radiographic magnification measures were based on the constant implant length. The shoulder of the implant was designated as a fixed index for calculating the degree of bone resorption. The level of marginal bone resorption is determined by the first point of contact between the bone and the implant in the mesial and distal area. The implant's shoulder's distance from the bone crest served as a benchmark for calculating the degree of bone resorption [Figure 1]. The distance between the shoulder of the implant and the bone crest was a standard for measuring the amount of bone resorption. The marginal bone resorption in the two groups was compared using three periapical radiographs taken immediately after crown cementation, 3 and 6 months after crown cementation.

Figure 1: Periapical radiograph for patient in group 1 representing bone loss after cementation, after 3 and after 6 months after crown insertion. Blue lines for standardization of the implant length and to determine the shoulder of the implant (the first contact between implant and bone), black lines determine the amount of marginal bone resorption.

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Results

Age and sex data showed normal (parametric) distribution. Statistical analysis of demographic data showed that there was no statistically significant difference between mean age values in the different groups. There was also no statistically significant difference between sex distributions in the different groups.

Numerical data were explored for normality by checking the distribution of data and using tests of normality (Kolmogorov–Smirnov and Shapiro–Wilk tests). All data showed non normal (nonparametric) distribution. Data were presented as median, range, mean, and SD values. Mann–Whitney U test was used to compare between the two groups. Friedman's test was used to study the changes by time within each group. Dunn's test was used for pairwise comparisons when Friedman's test is significant. The significance level was set at P value less than or equal to 0.05. Statistical analysis was performed with IBM SPSS Statistics for Windows, Version 23.0. (IBM Corp., Armonk, New York, USA).

Bone loss measurement (mm)

Mesial side

At crown cementation, after three as well as 6 months, there was no statistically significant difference between marginal bone loss in the two groups. As regards the changes in marginal bone loss of the two groups; there was a statistically significant change by time in marginal bone loss. Pairwise comparisons between follow up periods revealed that there was a statistically significant increase in marginal bone loss after 3 months followed by nonstatistically significant change from 3 to 6 months.

Distal side

After 3 as well as 6 months, there was no statistically significant difference between marginal bone loss in the two groups. As regards the changes in group I; there was a statistically significant change by time in marginal bone loss. Pairwise comparisons between follow up periods revealed that there was a statistically significant increase in marginal bone loss after 3 months followed by nonstatistically significant change from 3 to 6 months. While for group 2; there was a statistically significant change by time in marginal bone loss. Pairwise comparisons between follow up periods revealed that there was no statistically significant change in marginal bone loss after 3 months followed by a statistically significant increase in bone loss measurement from three to 6 months.

Overall bone loss (mean of the two sides)

After 3 as well as 6 months, there was no statistically significant difference between marginal bone loss in the two groups. As regards the changes in marginal bone loss of the two groups; there was a statistically significant change by time in marginal bone loss. Pairwise comparisons between follow up periods revealed that there was a statistically significant increase in marginal bone loss after 3 months followed by nonstatistically significant change from 3 to 6 months [Table 1].

Table 1: Descriptive statistics and results of Mann-Whitney U test for comparison between amounts of bone loss (mm) in the two groups

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Discussion

For patients who are completely or partially edentulous, implant dentistry is a safe and reliable therapeutic option. A microgap between the abutment and the implant and bacterial colonization are two factors that have been linked to CBL ^[2]. There have been conflicting reports on the impact of occlusal overload on the loss of bone around implants, and there is scant data to establish a cause-and-effect connection ^[3]. In general, overload is defined as an excessive occlusal load on an implant-supported FDP, which places a significant amount of stress on the surrounding bone tissue ^[4],[15]. The likelihood of CBL may rise if there is an imbalance in the occlusal load, which could lead to stress at the bone–implant coronal first contact site. ^[5]. Clinical studies have examined the existence of overload in connection to bruxism, tooth clenching, the length of the cantilever, or the presence of an implant-supported prosthesis as the antagonist ^[16],[17] nevertheless, the findings are challenging to duplicate and compare. Animal experiments produced conflicting results. In the presence of overload, it has been noted that there is an increase in marginal bone loss, a loss of osseointegration, or crater-like bone resorption. However, neither in healthy implants nor in implants afflicted by ligature-induced peri-implantitis in primates, did high loading produce any difference in histologically determined peri-implant bone loss. Although overload may affect how peri-implant bone behaves, it is yet unknown how overload affects the beginning and course of bone loss ^[18]. Therefore, this study was designed to evaluate the amount of bone resorption related to implant in free end saddle in response to different occlusal designs. Patients were evaluated for the amount of marginal bone level at the time of crown insertion, after 3 months of function and after 6 months. At the mesial side as well as the distal side, there was no statistically significant difference between marginal bone loss in the two groups. As regards the changes in marginal bone loss of the two groups; there was a statistically significant increase in marginal bone loss after 3 months followed by nonstatistically significant change from 3 to 6 months. Less than 0.2 mm of alveolar bone loss per year after the first year was one of the criteria for implant success, according to Ma et al. ^[19], alveolar bone loss was found to average 1.2 mm in the first year following abutment connection and to average about 0.1 mm per year after that for both the maxilla and the mandible. Older people and young adults both have peri-implant bone loss ^[20]. Stress can be transmitted to the bone–implant interface via occlusal load applied through the implant prosthesis and components. The amount of stress applied via the implant prosthesis is directly correlated with the degree of bone strain at the bone–implant contact. Beyond the physiologic limitations of bone, occlusal pressures may lead to strain in the bone significant enough to cause bone resorption. At stage 2 implant surgery, the bone is less dense and more fragile than it was a year later after prosthetic loading. At 4 months, bone is 60% mineralized, and the process takes 52 weeks to complete ^[20]. In the current investigation, bone loss occurred prior to loading, persisted for the first 3 months after loading, and then decreased for the next 3 months in both groups. Similar findings were presented by Trivedi et al. ^[20], who came to the conclusion that even after implant loading, there was considerable crestal bone modification even though CBL was higher prior to implant loading. This might be because the surrounding bone can adjust to the functional forces as they are applied to an implant. As a result, once the bone grows and gets denser, the occlusal pressure that initially causes bone loss (overload) is insufficient to continue to cause bone loss ^[20],[21]. Thongdee et al. ^[10] found that there was no significant difference in the relative occlusal forces between the implant protected occlusion and LOAD groups. The IPO group showed no significant difference in relative occlusal force between implant superstructure and contralateral natural tooth after 3–4 months of function. While in the LOAD group, the relative occlusal force between implant superstructure and contralateral natural tooth after 1–2 months of function was not significantly different. However, both groups showed that the relative occlusal force of implant restorations increased over time. Therefore, there was no significant difference between IPO and LOAD groups for marginal bone loss. Consequently, designing implant occlusion as group 2 which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown larger than the occlusal contact area of adjacent premolars, seemed to have the potential to be the optimum occlusion for implant since the marginal bone loss between the two groups did not show any significant differences. This implant occlusion design might help adjacent teeth to share occlusal loading better. Although we made an effort to reduce a number of the factors that contribute to marginal bone loss, it was difficult to regulate every one of them. Due to the small number of pertinent research, absence of buccal and lingual bone resorption assessment, high implant prices, lack of patient cooperation, and difficulties of long-term patient follow-up, it is still impossible to draw an unambiguous conclusion. Therefore, additional research with longer follow-up times is advised. Additionally, contemporary imaging methods like cone-beam computed tomography are more suitable for evaluating the bone surrounding the implant and provide more comprehensive data about all the surfaces.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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