Abstract
Aim:
To evaluate and compare the strain development and distribution of maxillary implant-supported complete fixed dental prosthesis (ISCFDP) with computer-aided design-computer-aided manufacturing milled PEEK BIO-HPP superstructure when placed using All-on-4 and All-on-6 situation using a strain gauge and finite element analysis (FEA).
Setting and Design:
This is an in vitro study to evaluate and compare the stress minimization and strain developed at implant in premolar and in two clinically simulated situation of All-on-4 and All-on -6 ISCFDP.
Materials and Methods:
The study involved converting a human skull into. stl format to create 3D-printed stereolithography models with a modulus of elasticity closer to bone. Implants were placed in two models (M1 nad M2) in incisor, premolar, and pterygoid regions. A fixed dental prosthesis framework was fabricated on both models, and strain gauge sensors were attached.
Statistical Analysis Used:
Descriptive and analytical statistics were done. The normality of data was analyzed by the Shapiro-Wilk test.
Results:
The results obtained were tabulated and it showed strain around the neck of ISCFDP under 100N configuration in strain gauge analysis. Stress was found more in the molar region when compared to the premolar region. This design showed that the largest stress around the neck of ISFDP under 100 N load was found more in the premolar region when compared to the molar region due to the reduction of stresses in the pterygoid region in FEA.
Conclusion:
In the present study, strain gauge analysis at 100 N for loading at the premolar and molar region shows the reduced strain on tilted implants in All-on-6 situation due to stress dissipation to the terminal pterygoid implant using strain gauge.
Keywords: Finite element analysis, implant-supported complete fixed dental prosthesis, pterygoid implant, strain gauge analysis
INTRODUCTION
The prosthetic rehabilitation of the atrophic maxilla is quite challenging since maxillary bone exhibits a centripetal mode of resorption accompanied by pneumatization of the maxillary sinus.[1]
All-on-4 technique, by Paulo malo brought a phenomenal change in the year 1996 to address full mouth rehabilitation for atrophic maxilla. This had limitations for having an appropriate cantilever A-P spread and short arch prosthesis.[2] To overcome this, shorter implants were in practice to provide support in the framework at the cantilever end.[3]
The shorter implants not only converted short arch prosthesis to conventional prosthesis but also provided support to the prosthesis.[4]
The pterygomaxillary region has proven to be a better anatomical area for the placement of implants with a good success rate, as it exhibits the least resorption.[4,5]
With the advent of multiunit abutments and the tilted implant concept, pterygoid areas were considered for placement of implants and provided support in full mouth rehabilitation cases.[6]
The purpose of this in-vitro study is to evaluate and compare the stress distribution of implant-supported maxillary complete fixed dental prosthesis when placed using the All-on-4 protocol with terminal cantilever and All-on-6 protocol with the support from terminal pterygoid implants by strain gauge and finite element analysis (FEA).
MATERIALS AND METHODS
Model preparation
A human skull was subjected to cone-beam computed tomography (CBCT), and the DICOM file was converted into. stl format to make a 3D printed model having a modulus of elasticity closer to bone through fused deposition modeling acrylonitrile butadiene styrene, Aaron Industries Corporation, AAROPRENE®, Gujarat, India, [Figure 1a-c]. These two 3D printed models (M1, M2) will serve as a standard for comparing the stress distribution on All-On-4 implant-supported complete fixed dental prosthesis (ISCFDP) and All-on-6 ISCFDP. Both models were coated with occlude spray (Diaswiss S. A, Switzerland) and subjected to Table top scanner (Shining 3D, India). The scanned images of M1 and M2 were superimposed on the computed tomography (CT) scan of 3D printed M1 and M2 for standardization of implant angulation in both models. A surgically guided stent (ANYCUBIC SLA UV-Curing 3D Printer Resin-B07G35CC1V, China) with sleeves for accommodating implant drills was printed [Figure 1a-c]. Ethical committee number Kcds/Ethical Comm/032/2020-2021.
Figure 1.
(a) Two 3D printed models M1 and M2 (b) surgical guide printed on M1 and M2 (c) Implant placement (d) Multiunit abutments of appropriate collar height were placed on M1 and M2 (e) Fixed dental prosthesis framework is fabricated on both M1 and M2
Virtual planning of implant position
Virtual planning was done to select the size of the implant in terms of diameter and length through CBCT data obtained from the patient.
Implant placement
In M1, using the surgical guide, two straight implants measuring 3.3/11 were placed at the incisor area, and two tilted implants measuring 3.75/13 were placed at the premolar area [Figure 1a-c]. In M2, the implants were placed the same as M1, along with two tilted implants measuring 3.75/16 mm were placed in the maxillary tuberosity area.
Fabrication of implant-supported complete fixed dental prosthesis
To establish a restorative platform for the prosthesis, a multi-unit abutment (Multi-unit Abutment, BioLine®) was placed on each implant in both M1 and M2 [Figure 1d]. Multi-unit scan bodies (Multi-unit Scan bodies, BioLine®) were placed on each implant, and both the models M1 and M2 were subjected to model scanning (Shining 3D – Table top scanner, Hangzhou, China). Peek framework was designed (Exocad GmbH, Darmstadt, Hessen, Germany) and was printed (Shining 3D ACCUFAB-D1S dental 3D printer, China) on both M1 and M2 followed by ceramic (Vintage Art, Shofu Inc.) layering [Figure 1e].
Strain gauge analysis
Attatching strain gauge sensors
In the laboratory, the buccal and lingual sides of the implant were bonded with a total of 10 strain gauges (TML JAPAN), which were equally spaced [Figure 2a-c].
Figure 2.
(a) Strain gauge sensors are placed on both the models M1 And M2 at the neck of each implant. (b) Vertical load applied bilaterally on model and developed up to 100N (c) Data acquisition system to determine strain values
Multi-stranded wires (TRI-COM Cables, U. S. A) with thin coatings, responsible for the electrical connections, were attached on the external surface, connecting the strain gauge sensors to an electrical signal conditioning unit (Data Acquisition System).
Loading conditions
Compression test was done to analyze the strain developed around each implant in both M1 and M2. A metal plate was kept on the model with ISCFDP for the uniform area of contact throughout. Both M1 and M2 were subjected to a vertical load of 100N for seven times using a universal testing machine (Model MCS 1000). The magnitude of strain on each strain gauge was recorded in units of micro strain [Figure 2a-c].
Finite element analysis
Meshing procedure
The simulated model of the maxillary jaw with implants and superstructure fabricated was scanned to obtain the image for FEM meshwork [Figure 3a and b]. The FEM meshwork has definite elements and nodes. The mesh model of the maxillary jaw created had an appropriate elastic modulus of bone and adjacent structures. This was subjected to appropriate masticatory load to evaluate stress concentration on two models of an All-on-4 situation and All-on-6 situation, and the data were tabulated [Tables 1 and 2].
Figure 3.
(a) Virtually designed 3D solid geometries of M1 and M2 model with implants and implant-supported complete fixed dental prosthesis (b) Mesh generation for both M1 and M2 using Ansys 18.1 software
Table 1.
Model description: Number of elements and nodes
| Model description | Elements | Nodes |
|---|---|---|
| All on 6 | 689,283 | 932,842 |
| All on 4 | 642,270 | 869,263 |
FEA: 100 N load was applied virtually in different positions and maximum principle stress was obtained. FEA: Finite element analysis
Table 2.
Stress distributed at 100N load in M1 and M2 using finite element analysis
| 100 N load/stress results | Peek | |
|---|---|---|
|
| ||
| All on 4 system | All on 6 system | |
| Overall deformation | 0.097397 | 0.00827 |
| Overall stress (Mpa) | 42.5866 | 19.2165 |
| Cortical stress (Mpa) | 35.1339 | 17.4645 |
| Cancellous stress (Mpa) | 1.85663 | 1.51403 |
| Implant stress (Mpa) | 53.4681 | 13.631 |
| Frame stress | 7.71444 | 2.56453 |
| Anterior implant stress (MPa) | 25.1218 | 13.631 |
| Posterior premolar implant stress (MPa) | 53.4681 | 11.5376 |
| Posterior molar implant stress (MPa) | - | 9.47419 |
Loading conditions
For the FEA, a vertical load of 100 N was applied bilaterally on each framework in M1 and M2. The load was divided equally on the posterior teeth to compensate for the difference in the number of teeth in the frameworks of the groups.
Stress analysis
The FEA was performed using Ansys18.1software (Ansys, Inc. Canonsburg, Pennsylavania). Cortical and cancellous bone stress, implant stress, framework stress, and overall deformation of the framework on 100N load application were evaluated.
RESULTS
The results obtained were tabulated in strain gauge analysis. 100 N vertical load was applied in different positions in M1 and M2 [Figure 2b]. Each test was repeated seven times as the sample size obtained was seven. Values obtained from the graph were subjected to statistical analysis and tabulated in different sets [Tables 3 and 4].
Table 3.
Numbering and positional placement of strain gauge in M1
| Gauge number | Position | Region | Microstrain | Strain |
|---|---|---|---|---|
| Gauge 1 | Buccal side | Premolar region (1st quadrant) | 493 | 0.000493 |
| Gauge 2 | Labial side | Incisor region (1st quadrant) | 146 | 0.000146 |
| Gauge 3 | Labial side | Incisor region (2nd quadrant) | 52 | 0.000052 |
| Gauge 4 | Buccal side | Premolar region (2nd quadrant) | 221 | 0.000221 |
Table 4.
Numbering and positional placement of strain gauge in M2
| Gauge number | Position | Region | Microstrain | Strain |
|---|---|---|---|---|
| Gauge 1 | Buccal side | Molar region (1st quadrant) | 238 | 0.000238 |
| Gauge 2 | Buccal side | Premolar region (1st quadrant) | 69 | 0.000069 |
| Gauge 3 | Labial side | Incisor region (1st quadrant) | 59 | 0.000059 |
| Gauge 4 | Labial side | Incisor region (2nd quadrant) | 74 | 0.000074 |
| Gauge 5 | Buccal side | Premolar region (2nd quadrant) | 169 | 0.000169 |
| Gauge 6 | Buccal side | Molar region (2nd quadrant) | 232 | 0.000232 |
In FEA, 100 N load was applied virtually in different positions, and maximum principle stress was obtained. The P value is equal to 0.05 [Table 5]. There is a significant difference between the All-on-4 system and All-on-6 system concerning peek [Tables 1 and 2]. The mean maximum overall stress observed in M1 v/s M2 [Figure 4a and b] due to the application of 100N load was compared. It was found that there a marginal significant difference existed in mean maximum overall stress observed at M1 v/s M2 due to the application of load on the PEEK maxillary ISCFDP.
Table 5.
P value of 100N in M1 and M2
| 100N load mean strain results | Peek | Statistic | |||
|---|---|---|---|---|---|
|
|
|
||||
| All-on-4 system | All-on-6 system | Mann–Whitney U | Z | P | |
| Mean | 228.00 | 140.17 | 30 | 2.45567 | 0.0364 |
| SD | 189.71 | 83.51 | |||
| Median | 183.50 | 121.50 | |||
Observation: The P value is nearly equal to 0.05. Inference: There is a significant difference between the all-on-4 system and the all-on-6 system concerning peek. SD: Standard deviation
Figure 4.
(a) Overall maximum stress in M1 (b) Overall maximum stress in M2
DISCUSSION
It is well known that prosthetic rehabilitation of the atrophic maxilla is quite challenging.[1] All on 4 technique, by Paulo Malo brought a phenomenal change in the year 1996 where in two straight implants were placed in the maxillary anterior region, and two tilted implants in the premolar region with accepted cantilever beam, favoring biomechanics of short arch prosthesis.[7] The limitations of this All-on-4 in terms of biomechanics were cantilever A-P spread and short arch prosthesis.[8,9] Meanwhile, the use of shorter implants to provide support in the framework of the cantilever was also in practice to convert the short arch prosthesis to a normal prosthesis.[5,6,10] Several studies have shown that the pterygoid region is resistant to resorption due to multiple muscle attachments, which provide torso frictional forces.[3,11,12] Further, with the advent of multi-unit abutments, a prosthesis can be envisioned with an excellent anchorage from the pterygoid region.[12] Implants placed in the posterior maxilla have been discussed as pterygoid plate implants, tuberosity implants, and pterygomaxillary implants. The structures that offer support for implant placement are the tuberosity of the maxillary bone, the pyramidal process of the palatine bone, and the pterygoid process of the sphenoid bone.[11,12]
Pterygoid implants are an alternative for treating patients with atrophic posterior maxilla because they have great success rates, comparable amounts of bone loss to conventional implants, few problems, and positive patient acceptability.[7-9]
Hence, in this study, the pterygoid region is utilized for the placement of implants for overcoming the limitation of All-on-4 techniques by comparing and evaluating the stress distributed and strain developed beneath ISCFDP in All-on-4 and All-on-6 situations using strain gauge and FEA
Physical model
This design showed strain around the neck of ISFDP under 100N configuration. Stress was found a little more in the molar region when compared to the premolar region, although when it was statistically compared result showed that the difference was insignificant.
Finite element model
This design showed that the largest stress around the neck of ISFDP under 100 N load was found more in the premolar region when compared to the molar region due to the reduction of stresses in the pterygoid region.
Strength of the study
Tilted implants are alternative without need of bone grafting. An implant in the posterior area aids in support to a cantilever beam, due to this, there is less deformation observed. Peek as a superstructure there is proven reduction of stresses to the bone through the implant.
Limitations of the present study and scope for future research
In this study, only a vertical load of 100N was tested and rotational and lateral forces that are exerted on implants and framework was not incorporated. The present study was done on the maxillary model. Further study can be done in the mandibular model.
CONCLUSION
Within the limitations of this study, the following conclusions are made:
In All-on-4 situation, the tilted implants placed in the premolar region exhibited more stress than the straight implants placed in the same situation
In the present study, statistical comparison of strain gauge analysis at 100 N for loading at premolar and molar regions revealed the reduction in strain developed on the tilted implants placed at the premolar area when placed in an All-on-6 situation due to dissipation of stress to the terminal pterygoid implant using a strain gauge
Implants placed in All-on-6 situation had a better distribution of stress than implants placed in All-on-4 situation
Peek framework in All-on-4 situations had higher stress than All-on-6 situations
In FEA, when a load of 100 N was applied, the stress was seen higher in the neck of ISCFDP of the premolar region when compared to the molar region.
M1 and M2
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Candel E, Peñarrocha D, Peñarrocha M. Rehabilitation of the atrophic posterior maxilla with pterygoid implants: A review. J Oral Implantol. 2012;38:461–6. doi: 10.1563/AAID-JOI-D-10-00200. [DOI] [PubMed] [Google Scholar]
- 2.Nag PV, Sarika P, Bhagwatkar T, Dhara V. Pterygoid implant: Option for rehabilitation of the atrophic posterior maxilla. Int J Contemp Dent Med Rev. 2019:1–5. [Google Scholar]
- 3.Bidra AS, Huynh-Ba G. Implants in the pterygoid region: A systematic review of the literature. Int J Oral Maxillofac Surg. 2011;40:773–81. doi: 10.1016/j.ijom.2011.04.007. [DOI] [PubMed] [Google Scholar]
- 4.Albrektsson T, Zarb G, Worthington P, Eriksson AR. The long-term efficacy of currently used dental implants: A review and proposed criteria of success. Int J Oral Maxillofac Implants. 1986;1:11–25. [PubMed] [Google Scholar]
- 5.Ogawa T, Dhaliwal S, Naert I, Mine A, Kronstrom M, Sasaki K, et al. Effect of tilted and short distal implants on axial forces and bending moments in implants supporting fixed dental prostheses: An in vitro study. Int J Prosthodont. 2010;23:566–73. [PubMed] [Google Scholar]
- 6.Ratna Nag P, Sarika P, Khan R, Bhagwatkar T. Ttphil-all tilt™–an effective technique for loading of dental implants: A comparative study of Stress distribution in maxilla using finite element analysis. J Dental Implants. 2019;9:4–11. [Google Scholar]
- 7.Assif D, Marshak B, Horowitz A. Analysis of load transfer and stress distribution by an implant-supported fixed partial denture. J Prosthet Dent. 1996;75:285–91. doi: 10.1016/s0022-3913(96)90486-2. [DOI] [PubMed] [Google Scholar]
- 8.Zoidis P. The all-on-4 modified polyetheretherketone treatment approach: A clinical report. J Prosthet Dent. 2018;119:516–21. doi: 10.1016/j.prosdent.2017.04.020. [DOI] [PubMed] [Google Scholar]
- 9.Tashkandi EA, Lang BR, Edge MJ. Analysis of strain at selected bone sites of a cantilevered implant-supported prosthesis. J Prosthet Dent. 1996;76:158–64. doi: 10.1016/s0022-3913(96)90300-5. [DOI] [PubMed] [Google Scholar]
- 10.Akça K, Iplikçioğlu H. Finite element stress analysis of the effect of short implant usage in place of cantilever extensions in mandibular posterior edentulism. J Oral Rehabil. 2002;29:350–6. doi: 10.1046/j.1365-2842.2002.00872.x. [DOI] [PubMed] [Google Scholar]
- 11.Krekmanov L, Kahn M, Rangert B, Lindström H. Tilting of posterior mandibular and maxillary implants for improved prosthesis support. Int J Oral Maxillofac Implants. 2000;15:405–14. [PubMed] [Google Scholar]
- 12.Maló P, Rangert B, Nobre M. “All-on-Four”immediate-function concept with brånemark system implants for completely edentulous mandibles: A retrospective clinical study. Clin Implant Dent Relat Res. 2003;5(Suppl 1):2–9. doi: 10.1111/j.1708-8208.2003.tb00010.x. [DOI] [PubMed] [Google Scholar]