Effect of Inter-Implant Distance on Fracture Resistance of Implant-Supported Provisional Fixed Dental Prosthesis
This study aimed to identify the ideal interimplant distance for optimum outcome on immediately loaded implant supported prosthesis. Hence this study was taken up to analyze the effect of varying interimplant distance on fracture resistance of implant supported provisional fixed dental prosthesis (FDP). A total of 24 bis-acrylate composite resin samples were prepared. Interimplant distance was present in the metal die for placement of dummy implants at distances of 14 mm, 21 mm, and 30 mm respectively. Wax-up for 3-unit, 4-unit, and 5-unit implant-supported provisional restoration was made. Silicone molds were used for making multiple interim prostheses using bis-acrylate composite material. All samples were subjected to fracture test in the universal testing machine with a crosshead speed of 1 mm/min. All samples were loaded with gradual force starting from 100 N until it fractured. The load was applied at the center of prosthesis. Data was analyzed by one-way analysis of variance and Bonferroni post hoc test. Mean fracture resistance of 3-unit provisional FDP at 14 mm of interimplant distance showed 1342.61 ± 179.15 N. Mean fracture resistance of 4-unit provisional FDP at 21 mm of interimplant distance showed 1420.44 ± 170.37 N. Mean fracture resistance of 5-unit provisional FDP at 30 mm of interimplant distance showed 791.61 ± 203.59 N. Both 14 mm and 21 mm of interimplant distance are suitable span lengths to be considered for the optimum outcome during immediately loading with implant-supported provisional restorations. Limitations of the study were that force application was static in nature and not dynamic and the arch form was not “U” shaped but longitudinal using Bis-Acryl material only with no cantilever. Future studies can be done to evaluate the fracture resistance of bis-acrylate material considering biomechanics and arch form of natural dentition. Distal cantilever should be considered along with different material for fabricating provisional restoration.
Introduction
Tooth loss is common in geriatric patients leading to completely edentulous condition in 16.3% of Indian population.1 When patient are completely edentulous there is negative impact on patients nutritional status along with loss of confidence as there is impairment of speech, esthetics, and functional requirement. Fixed implant-supported treatment option is a viable alternative in completely edentulous patients to help in gaining confidence.
In implant dentistry, immediate loading has gained popularity because of decreased overall treatment time for achieving the esthetic and functional requirement. Full-arch immediate loading are usually carried out with 4–8 implants depending on the volume and density of available bone. Self-cure resins have been widely used for provisionalization in clinical practice. During immediate loading, provisionalization is a critical step as the material needs to be functionally and also esthetically fulfill the requirements.2 A rigid provisional restoration can potentially lessen the stress on the implant and hence minimize micromovements.3 The provisional prosthesis should meet all the requirements of esthetics, function, and durability.4
Bis-acrylate resin has gained attention because it is available as an auto mix cartridge-based dispensing system. In addition to the low polymerization shrinkage and less leaching of residual monomer, bis-acrylate materials have a less exothermic setting reaction and are hydrophobic in nature, which offers them an advantage over poly (methyl methacrylate) (PMMA) materials.5 The distinct monomer content of bis-acrylate resins and methacrylate resins accounts for the majority of the variances in their flexural strengths.6
The drawbacks of PMMA temporary fixed dental prosthesis (FDPs) is that they are prone to fracture because of their inadequate mechanical strength and due to longer interimplant distance, when they are subjected to high occlusal forces.7 They exhibited decreased flexural strength because of high water absorption. Clinicians are typically inconvenienced by the recurrent mechanical failures of provisional fixed prostheses since it takes more chairside time to repair or rehabilitate FDPs. Depending on the aging, wear processes, fatigue, and water absorption, the provisional material is selected to overcome the risk of fracture.4
This research focuses on a full-arch provisional restoration supported by four dental implants in completely edentulous arch. For occlusal load distribution, cantilever length and anterior-posterior (A-P) spread are essential factors to be considered.8 The A-P spread of the implant should be considered to calculate the distal cantilever length of the entire arch.9 For immediately loading in completely edentulous arch, a minimum of 4 implants is required for acceptable clinical outcome. So with varying interimplant distance between 2 implants, the most suitable span length for provisional FDP to withstand the occlusal load without fracture of the prosthesis needs to be analyzed. Rationale of the study is to evaluate optimum A-P spread to overcome the problems of fracture during the immediate loading phase. Research question of the study is “What is the ideal interimplant distance for completely edentulous arch where immediately loading is considered?”.
Research on the fracture pattern and fracture load of fiber-reinforced temporary FDP at various pontic span lengths has been conducted; however, studies investigating the fracture resistance of bis-acrylate-based implant-supported provisional FDP at varying interimplant distances and the most suitable span length for optimum outcome of provisional implant-supported FDP have not been conducted. Hence this study was done to analyze the effect of varying interimplant distance on fracture resistance of implant-supported provisional FDP. The aim of the study is to evaluate the fracture resistance of implant-supported provisional fixed dental prosthesis with varying inter-implant distance. The objectives of the study are to evaluate and compare the fracture resistance of provisional fixed dental prosthesis at 14 mm, 21 mm, and 30mm of interimplant distance.
Null hypothesis-varying interimplant distance does not have effect on fracture resistance of implant supported provisional FDP. Alternative hypothesis-varying interimplant distance significantly affects fracture resistance of implant-supported provisional FDP.
Materials and Methods
A stainless steel metal die was fabricated to simulate the completely edentulous scenario with implant-supported provisional FDPs. Interimplant distance was present in a metal die for placement of dummy implant at distances of 14 mm, 21 mm, and 30 mm, respectively. (Figure 1) Implants (Adin 4.2 × 11.5 mm, ISF 1142) were placed in subsequent holes. The straight abutments (REF RS3801) was attached to the dental implant with the help of implant-abutment screw. A total of 24 samples were prepared using bis-acrylate composite resin material (Qu resin Pink, REF 540 0116 1, Bredent). There were 3 groups present. Each group will have 8 samples with pontic height of 7 mm and connector height of 4.3 mm.
Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00055
Wax pattern (Geo Crowax, Renfert) for 3-unit, 4-unit, and 5-unit implant-supported provisional restorations were made. A silicone index was fabricated using high precision condensation silicone (Zeta Plus, Zhermack) as a template for a provisional restoration (to maintain standardization with respect to dimension of samples). Interim prosthesis were fabricated for each groups by injecting a bis-acryl automized cartridge into silicone mold to construct the samples of various span lengths. Consistency and proportion of bis-acrylate composite resin samples was standardized with Auto-Mix cartridge-based system. Reliability of dimension of bis-acrylate samples was controlled using condensation silicone index. (Index accuracy was maintained using proper base and catalyst ratio according to the manufacturer instructions.) Bis-acrylate samples dimension was cross-checked using vernier caliper. In the first group, 3-unit implant-supported bis-acryl based provisional restorations were prepared at 14 mm of interimplant distance. In the second group, 4-unit implant-supported bis-acryl based provisional restorations were prepared at 21 mm of interimplant distance. In the third group, 5-unit implant-supported bis-acryl based provisional restorations were fabricated at 30 mm of interimplant distance (Figure 2) Every sample was rubbed for 20 seconds using gauze that had been soaked in alcohol. All the provisional restorations were trimmed with acrylic carbide burs and acrylic stone bur. After that, sandpaper was used. Finishing and polishing of all samples was done with the help of pumice of wet slurry after which a muslin buffing wheel was used.
Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00055
Fracture resistance test
All samples were subjected to fracture test to measure the fracture resistance. The test was performed using a Universal Testing Machine (Zwick/Roell Z020). The load was applied using a stainless steel spherical load parallel to the long axis of implants at the center of all prosthesis (Figure 3). The crosshead speed was 1.0 mm/min. A gradual load was applied to all the samples starting from 100N until it fractures, and the load (N) at failure was recorded when there was either a marked decline in the load curve and a visual or audible evidence of fracture (Figure 4).
Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00055
Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00055
Statistical method of analysis
The statistical methodology was reviewed and approved by an independent statistician. The data was checked for normality using Shapiro-Wilk test and it was found to be normally distributed. Descriptive statistics were expressed as mean and standard deviation. One-way analysis of variance (ANOVA) was used to find comparison of mean fracture resistance between 3 groups. Bonferroni post hoc test was carried out to determine the effect of difference in length on fracture resistance if ANOVA showed overall significances. The Bonferroni method tolerates Type I error. The data was statistically analyzed using SPSS Software version 23. G* Power software version 3.1 was used to calculate the sample size of 24. For all statistical tests, P < .05 was considered as statistically significant, keeping the margin of the error at 5%, thus giving 90% power of the study.
Results
The present study was carried out to compare and evaluate the fracture resistance of implant-supported provisional restoration with varying interimplant distance. The results are statistically analyzed and presented in Tables 1 and 2.
In Table 1, after a fracture resistance test, provisional restoration with 14 mm of interimplant distance showed mean fracture resistance of 1342.61 N ± 179.15 N (Group 1). After increasing the interimplant distance from 14 mm to 21 mm, mean fracture resistance increased to 1420.44 ± 170.37 N for Group 2 samples. But further increasing the interimplant distance from 21 mm to 30 mm, showed a decrease in fracture resistance values to 791.61 ± 203.59 N for Group 3 samples.
There was no statistical significant difference in deformation at break values between the 3 groups, but there was overall significant difference for fracture resistance (Fmax) and peak detection values.
Figure 5 depicted the graphical representation of maximum fracture resistance and peak detection values of samples with 14 mm, 21mm, and 30 mm of interimplant distance samples. Table 2, dtatistical significant difference was observed in Fmax and peak detection between interimplant distance of 14 mm vs 30 mm and 21 mm vs 30 mm. No statistically significant difference was observed between interimplant distance of 14 mm vs interimplant distance of 21 mm.
Citation: Journal of Oral Implantology 50, 5; 10.1563/aaid-joi-D-24-00055
Discussion
Immediately loading with rigid provisional restoration is considered a successful treatment option if the primary stability of implants is adequate. During the healing period the micromovements should be within the physiologic limits (less than 100 µm). The implant macro and micro design and its geometry will influence the primary stability, and its surface treatment will affect the bone-implant interface in immediately loaded cases. Hence implant design, its surface treatment, number of implants, implant length, available bone quality, bone quantity, occlusal scheme, anterioposterior spread of implant, and cantilever length are important parameters to be considered during immediate functional loading. According to Romanos et al, immobilization of all the implants by rigid splinting should be managed for 3 months for long-term success in immediate loading cases.10
Immediate loading with all-on-4 concept had gained attention because of the cost and reduced overall treatment duration. It has several merits such as improved esthetics and functional requirements, psychological acceptance with gained confidence, superior soft tissue healing, fast postoperative recovery, and elimination of problems associated with removable prosthesis.11
Horita et al studied the biomechanical behavior of 4 immediately loaded implants using the “all-on-four” concept in an edentulous mandible. They discovered that in the immediately loading model, the micromotion seen at the bone-implant connection ranged from 7.5 µm to 14.4 µm and it was within the permissible limits for uninterrupted implant ossteointegration.12 Yamaguchi et al evaluated the implant displacement and the corresponding stress on the surrounding bone under the loading circumstances using finite element analysis (FEA) study. The rigid provisional restoration with reinforcement decreases the amplitude of displacement of the implant significantly (mean reduction displacement amplitude was 37.2µm ± 7.4µm) and reduces the stresses at the implant-bone interface and has better occlusal force distribution with rigid framework, which improves cross-arch stabilization.3
The present study aimed to evaluate the effect of varying inter-implant distance (A-P spread) on the fracture resistance of the bis-acrylate based implant-supported provisional restorations. In the current study occluso-gingival height was maintained constant with pontic height of 7 mm, connector height of 4.3 mm, and changed the interimplant distance to verify its effect on the mechanical property of bis-acrylate composite material.
Fracture resistance was calculated using the universal testing machine, which helped to gauge when the fracture line was initiated (peak detection) and how much load the restoration can tolerate until it finally fractures after visual or audible evidence of fracture (Fmax). During load application rate of deformation of provisional restoration was also analyzed along with Fmax and peak detection. The mean fracture resistance of samples with 14 mm interimplant distance showed 1342.61 ± 179.15 N. After increasing the interimplant distance from 14 mm to 21 mm, mean fracture resistance increased to 1420.44 ± 170.37 N. But further increasing the interimplant distance from 21 mm to 30 mm, showed a decrease in fracture resistance values to 791.61 ± 203.59 N. Differences in mean fracture resistances values between 14 mm and 21 mm of interimplant distance was 78 N and standard deviation was 9 N. There was not much difference between the two. One-way ANOVA showed overall significance, and post hoc test showed that there was no statistically significant difference between 14 mm vs 21 mm in terms of fracture resistance. The null hypothesis was rejected as increasing interimplant distance between 14 mm to 21 mm does have significant effect on fracture resistance of implant-supported provisional FDPs. However, at 30 mm of interimplant distance fracture resistance significantly decreased. Thus alternative hypothesis was accepted.
Analyzing the results of peak detection (initial fracture in the restoration or the point at which failure was recorded when there was a marked decline in the load curve), samples with 14 mm of interimplant distance showed peak detection at 1225.18 ± 276.34 N, whereas at 21 mm of interimplant distance, samples showed peak detection value at 993.37 ± 295.67 N. This means samples with 14 mm of interimplant distance can resist more load before the initial fracture begins, as compared to 21 mm of samples. While comparing maximum fracture resistance values, the maximum fracture load tolerated by 21 mm samples was much higher than 14 mm of samples as mentioned above. But statistically, there was no significant difference between 14 mm samples vs 21 mm samples in terms of fracture resistance (Fmax) and peak detection values. Whereas for 30 mm of interimplant distance samples, peak detection (492.62 ± 104.97 N) and fracture resistance values shown was lower than others. 30 mm samples showed peak detection at 492.62 N, which means they can hold up lesser load compared to 14 mm and 21 mm of samples.
Deformation of material depicted the rate at which material can bend or flex before permanent deformation results. Deformation at break values means the point at which the material was no longer in its elastic state and showed permanent deformation. Mean rate of deformation of samples with 14 mm interimplant distance was 1.16 mm, 21 mm of interimplant distance was 1.37 mm, whereas 30 mm of interimplant distance was 1.19 mm. Considering deformation at break values of all 3 groups, there was no statistically significant difference between them. Deformation of the material was similar for all the groups irrespective of its length.
The present study evaluated fracture resistance of provisional restoration using 3 different span lengths. Interimplant distance from center of one implant to center of other implant was considered. The initial fracture (initial point at which there was a marked decline in load curve) was considered as peak detection value of the samples. According to our findings at 21 mm of interimplant distance the material can endure more load compared to 30 mm of interimplant distance. Comparing our study with a study by Chang et al, by applying a similar concept to our study, the pontic span length considered in this study was 20.75 mm, 23.75 mm, 26.75 mm, and 30.75 mm measured from center of mesial abutment to center of distal abutment. In this study, initial fracture was considered as fracture load of the sample. The mean fracture load of unreinforced acrylic provisional FDP at 20.75 mm of span length was 666.17 ± 91.1 N and at 30.75 mm of span length was 293.5 ± 75.4 N. In contrast to our investigation, the Chang et al study reported significantly lower fracture resistance values because of thermal cycling and repeated loading. The reason for the contradiction between the findings of fracture load values are mainly because of different material used by the previous study, which has distinct properties. The material employed by Chang et al was Poly (methyl methacrylate) whereas material used in our study was bis-acrylate composite resin.7 This is in contrast to an investigation by Chen et al, in which the mean fracture load for 4-unit provisional restoration without reinforcement was 413.3 N ± 63.5 N after thermocycling at 26.75 mm of interabutment distance. According to our investigation, 21 mm of interimplant distance samples showed optimal outcome in terms of maximum fracture resistance. The above findings of Chen et al are in alignment with the present study.13
In the study, axial static force of 100 N was applied at the center of all prosthesis and then load was increased gradually until it fractures. The mean fracture resistance was highest for samples with 21 mm of interimplant distance. It can be interpreted that the load tolerated at this A-P spread was better compared to 30 mm of interimplant distance. It can also be stated that 21 mm of samples will take more time to fracture, which means they can resist more forces until they failed intraorally. While correlating our study with the Seth et al study, they performed a stress analysis FEA study and concluded that at 19 mm of interimplant distance the stresses observed in the implant were maximum under all loading conditions. But during axial loading, 21 mm of interimplant distance showed less stress, which is in line with our study. These findings of Seth et al research are in comparison with the current study.14
In research, the rate of deformation of 4-unit implant-supported bis-acrylate based provisional restoration was 1.37 ± 0.17 mm. The study outcomes are inconsistent with the Borie et al study. They revealed that the rate of deformation of 4-unit implant-supported acrylic prosthesis was 0.13–0.254 mm. The reason for contradictory findings is mainly because of differences in load application. The load applied in our in vitro study was axial static load of 100N at the center of the posterior prosthesis, whereas in this FEA study, the load applied was oblique static load of 150N, at cingulum area of upper incisors. The material used in the study was bis-acrylate composite resin to fabricate provisional prosthesis; on the other hand, the FEA study by Borie et al employed heat cure acrylic resin to fabricate fixed prosthesis.15
The provisional implant-supported FDPs at 14 mm and 21 mm of interimplant distance showed initial fracture at 1225.18N and 993.37 N, respectively. These force values are above the usual force endured by the implant-supported prosthesis in an oral environment. Thus this leads us to the conclusion that the best span lengths to take into account for immediately loading situations are 14 and 21 mm of interimplant distance, as they will be able to sustain the heavy occlusal load without breaking. This in turn reduces the risk of fracture results into reduced micromoments at the implant-bone interface throughout the healing phase. While discussing the 30 mm of interimplant distance, the initial fracture resistance value recorded was 492.62 N, which was below the normal biting force borne by implant-supported prosthesis intraorally. It is not recommended to use an interimplant distance of 30 mm when contemplating long-span implant-supported provisional restorations during immediate loading cases. While correlating our study with a study by Al-Omiri et al, they concluded that the mean maximum occlusal bite force noted at implant-supported bridge side was 577.9 ± 78.5 N and at dentate side, 595.1 ± 74.9 N. These results are contradicting our study results. The reason for conflict is because the study was conducted using rigid die to simulate completely edentulous scenario, which does not exactly mimic intraoral environment, and biomechanics was not considered, whereas the research by Al-Omiri et al was performed in human subjects.16
The strength of the study is characterized as inter-implant distance of 30 mm was considered in study which was not addressed by other studies, 30 mm span length usually contemplated in clinical scenario (where 1 implant was placed in lateral incisor region and one in molar region). The study addressed what was the maximum span length during immediate loading to get optimum outcome. Study results are applicable in clinical scenarios as the power of the study was 90% and margin of error was 5%. Characteristics of material will not change according to the changes in environment.
Conclusion
Both 14 mm and 2mm of interimplant distance are suitable span lengths to be considered for the optimum outcome during immediate loading with implant-supported provisional restoration. It is not recommended to use an interimplant distance of 30 mm while considering long-span implant-supported provisional restorations during immediate loading. Bis-acrylate composite resin is a suitable material for fabrication of provisional restoration during immediate loading.
Limitations of the study
In our study, axial loading was considered. The force application was static in nature, which does not mimic the intraoral environment in which dynamic forces are acting. In this study we did not consider the arch of the natural dentition; instead, we used the longitudinal model. Biomechanics is not considered as this is an in vitro study in which a rigid metal die was used, whereas using human cadaver bone or in vivo studies can be considered for biomechanics and arch form of the natural dentition which might give us different results. Distal cantilever should be considered along with different material for fabricating provisional restoration. Using different materials for provisional restoration can lead to different outcomes. The fracture resistance values would differ accordingly. In the present study distal cantilever forces are not considered.
Scope for future work
This study was conducted on metal die to simulate the completely edentulous scenario. Future studies can be done to evaluate the fracture resistance of bis-acrylate material considering biomechanics and arch form of natural dentition. Distal cantilever should be considered along with different material for fabricating provisional restoration.
In situations where there is an ideal interarch space of 30 mm, where pontic height will be 15 mm, and the connector height of 12 mm will be present, it will increase the strength of the material. which can minimize the fracture when 30 mm of interimplant distance is present for which further studies can be done.
(a) Metal die simulating completely edentulous condition. (b) Image showing interimplant distance of 14 mm. (c) Image showing inter-implant distance of 21 mm. (d) Image showing interimplant distance of 30 mm.
(a) 3-unit implant-supported fixed provisional restoration. (b) 4-unit implant-supported fixed provisional restoration. (c) 5-unit implant-supported fixed provisional restoration.
Fracture resistance tested using universal testing machine.
(a) and (b) Showing fracture of the implant-supported provisional restorations.
Graphical representation of maximum fracture resistance and peak detection values of samples with 14 mm, 21 mm, and 30 mm of interimplant distance samples. Error bars representing standard deviation.
Contributor Notes