|Year : 2021 | Volume
| Issue : 2 | Page : 38-44
Comparative study between different designs of maxillary implant assisted overdenture (in vitro study)
Samar H Makled, Fadel A Abd Elfatah, Mohamed N El-Guindy
Department of Prosthetic Dentistry, Faculty of Dentistry, University of Tanta, Tanta, Egypt
|Date of Submission||19-Jun-2019|
|Date of Decision||30-Sep-2019|
|Date of Acceptance||12-Jul-2021|
|Date of Web Publication||15-Sep-2021|
MSc Samar H Makled
Department of Prosthetic Dentistry, Faculty of Dentistry, University of Tanta, Tanta 31527
Source of Support: None, Conflict of Interest: None
Evaluate microstrains on peri-implants tissue of different designs of maxillary complete overdenture assisted by different number of implants.
Two maxillary epoxy resin models used, for the first model two implants with 4.5 mm diameter and 13 mm length installed in the canine area and two implants with 4.5 mm diameter and 10 mm length installed in the second premolar area and two designs of maxillary overdenture used: group I maxillary implant overdenture (MIOD) assisted by four implants and Group (II) palateless maxillary implant overdenture assisted by four implants, for the second model two implants with 4.5 mm diameter and 13 mm length installed in the canine area and two designs of maxillary over denture used: group III MIOD assisted by two implants and group IV palateless implant overdenture assisted by two implants, four strain gauges used around each implant, bilateral static 100 N vertical load and 65 N oblique load applied on the occlusal surface of each MIOD. Stress meter used to measure the microstrains using software (ED × 10 A).
The least stress found related to group I under 100 N vertical loading and the highest readings found related to group IV under 65 N oblique loading, under vertical loading stresses recorded in group III was greater than group I, stress in group IV was greater than group II, stress in group II was greater than group I, stress in group IV was greater than group III, under oblique loading, stress in group III was greater than group I, stress in group IV was greater than group II, stress in group II was greater than group I, stress in group IV was greater than group II.
Removing the palatal part from MIOD could be done in case of using four implants without damaging the prei-implants tissues.
Keywords: equator, implant, maxillary overdenture
|How to cite this article:|
Makled SH, Abd Elfatah FA, El-Guindy MN. Comparative study between different designs of maxillary implant assisted overdenture (in vitro study). Tanta Dent J 2021;18:38-44
|How to cite this URL:|
Makled SH, Abd Elfatah FA, El-Guindy MN. Comparative study between different designs of maxillary implant assisted overdenture (in vitro study). Tanta Dent J [serial online] 2021 [cited 2021 Oct 19];18:38-44. Available from: http://www.tmj.eg.net/text.asp?2021/18/2/38/326035
| Introduction|| |
Conventional dentures have been the primary treatment choice for the rehabilitation of completely edentulous patients. Although most of the patients are satisfied with this treatment, many have difficulties adjusting to wearing dentures or are dissatisfied with them ,.
Implant overdenture treatments for the edentulous maxilla is challenging, as several complications have been reported with maxillary implant overdenture (MIOD). Poor bone quality, low bone quantity, short implant length, and poor initial stability are inherent anatomic and biomechanical problems encountered in the edentulous maxilla which may be responsible for high implant loss susceptibility and, so the loss of retention of MIOD , and have been registered with a high implant failure compared to other implant treatment modalities over 20% .
As a rational reason to up grading the number of the maxillary implant due to many factors conclude the main success expectation depending on the bone foundations which becomes worth by two to three times with the reclined maxillary bone type according to the Lekholm and Zarb bone scales ,,. A minimum of four or two well-spaced implants is often recommended for an implant-supported and retained-overdenture. The increased number of implants in the maxilla compared to the mandible is due to the softer bone which is present in maxilla and the distribution of occlusal forces .
In case of using four unsplinted implants to support MIOD with partial palatal coverage, implants must not be less than 10 mm long and 3.75 mm implant wide . A minimum of 13 mm implant length and 3.8 mm implant diameter for MIOD with a horseshoe design . Implant distribution regardless the number shares on the load overcoming. A broadly distributed implant-supported design has been recommended in favor of a concentrated array of implants in the anterior region. Placing double implants in the canine area and in the first molar area is acceptable to over stand the exaggerated forces ,. Anteriorly, canine area is a key implant position while posterior key implant position is still controversial . Positioning the implants in anterior maxilla, mesial to the first premolars enhances the stability of the overdenture, for a design without palatal coverage .
Implant removable overdentures allow reduced flanges and palate of maxillary prosthesis when the overdenture supported by four implants in case of successful implant placement and healing. There is no need for palatal coverage since the stress on implants will be clinically acceptable ,.
Many authors recommended the palateless denture as subjective treatment of the gagging reflex with the accompanying consideration of solving retention and support problems ,,. OT-equators can be used in all clinical scenarios that require an implant supported crown, bridge or complete overdenture, yet their smaller size makes them uniquely suited for tight places or where space is limited, especially for overdentures, OT-equators provide good stability and retention, plus improved esthetics and reduced residual ridge resorption, with as few as two to four implants; reducing both the trauma and high cost associated with placing more implants . The most common complications related to the natural dentition are primarily biologic in nature (e.g. periodontal diseases, caries and pulp pathology) .
Many studies revealed that an essential step in the analysis of loading, is to analyze the force transfer at the implant–bone interface. It is essential that both implant and bone are stressed within a certain range. Overstressing can cause bone resorption or fatigue failure under loading of the bone may lead to disuse atrophy and therefore to bone loss as well ,,. This study aimed to evaluate microstrains on peri-implants tissues of different designs of maxillary complete overdenture assisted by different number of implants using equator attachment.
| Methods|| |
Two readymade identical maxillary completely edentulous epoxy resin models (Ramses Co., Alexandria, Egypt) were used with area representing the ridge and the vault covered by 2 mm of flexible polyurethane layer simulating oral mucosa [Figure 1]. For the first model (A) four implants (Megagen, Seoul, Korea) were placed two in the canine region and two in the second premolar region and two designs of maxillary overdenture were made and according to this model A classified into two groups:
- Group I: MIOD assisted by four implants.
- Group II: palateless implant overdenture (PIOD) assisted by four implants.
For the second model (B) two implants was placed in canine region two designs of maxillary overdenture were made and according to this model (B) classified into two groups:
- Group III: MIOD assisted by two implants.
- Group IV: PIOD assisted by two implants.
Each cast was held in a vertical milling machine (Milling and Drilling Machine, TUV, India) , to ensure parallelism of the installed implants [Figure 2]. Surgical drilling bur with 4 mm diameter was used to drill the holes.  For the first model four holes were drilled, two in canine region with 13 mm depth, and two in second premolar regions with 10 mm in depth on both sides and for the second model two holes were drilled in canine region with 13 mm in depth. Megagen implant system was used, two implants 4.5 mm diameter and 13 mm length were inserted in the canine region in the two models, two implants 4.5 mm diameter and 10 mm length were inserted in the second premolar region for the first model.
The trial denture was waxed up then processed into heat cured acrylic resin, finished, polished, and adjusted on the epoxy resin model. To make four identical upper complete dentures, one denture was made then duplicated three times to get two MIOD and two PIOD. Each implant received OT-equator attachment: model A [Figure 3] and model B [Figure 4] OT-equator attachment picking up (direct technique). Silicon rubber ring was attached to each attachment as a spacer to prevent escape of self-cure acrylic resin in the undercut beneath the attachment.
Marks were done in the fitting surface of each denture opposite to each attachment by using pressure indicating past and then relief was made at these points on the fitting surface of the denture. The OT-equator metal caps were seated on the OT-equator abutment, auto-polymerizing acrylic resin was packed into the relieved areas in the complete denture to hold the OT-equator cap.
The strain gauges (Electronic Instrument Co Ltd, Tokyo, Japan) were used for this study. For each model four tunnels (2 mm in diameter and 4 mm in length) were prepared in the epoxy resin model just around the implant surface parallel to the long axis of the implant in mesial, distal, buccal and palatal surfaces, four strain gauges installed in each tunnel, model A [Figure 5] and model B [Figure 6].
A strain gauge adhesive (CC-33 strain gauge cement; Kyowa Electronic Instrument Co. Ltd, Tokyo, Japan.) was used to cement the strain gauges on the epoxy resin parallel to the long axis of the implant and held in their sites for 5 min. The wires of the strain gauges were connected to a digital multichannel strain meter (Kyowa Electronic Instruments Co. Ltd) [Figure 7]. The strain meter was connected to a compatible lap top containing the meter control software (ED × 10 A).
Each of the two models placed on the base of the loading device of universal testing machine (Instron 3365, UK) and then: the vertical load measurement [Figure 8] every model was placed with the overdenture in its place in a horizontal plane of the base of the loading device base and bilateral static 100 N vertical load was applied. The oblique load measurement: every model were placed with the overdenture in its place on the surface of an oblique wooden segment which made angle equal 35° with the applied load and bilateral static 65 N oblique load was applied. Point of load application was the center of X shape metal bar resting on the occlusal surface. The forces were delivered to the center of the metal bar using a loading pin (applicator) attached to the digitalized testing machine.
The load is applied 10 times for each model vertically and also obliquely to ensure the reproducibility of the results with at least 5 min' interval between the readings to allow relief of formed strains before making the next reading. The strain readings were transferred to strain units. Data were analyzed using software (ED × 10 A). The mean of the values recorded from the four strain gauges around the implants were used for stress evaluation using 100 N vertical load and 65 N oblique load. Statistical analysis of the present study was collected, tabulated using the mean, SD, Student t test by SPSS V17 software program.
Approval for this research was obtained from the Research Ethics Committee, Faculty of Dentistry, Tanta University. The design and procedures of the present study were accomplished according to the research guidelines published by the Research Ethics Committee, Faculty of Dentistry, Tanta University.
| Results|| |
The results showed the mean of the values recorded from the four strain gauges at the buccal, lingual, mesial and distal around each implant under bilateral 100 N vertical load and 65 N oblique load for groups I, II, III and IV.
[Table 1] and show the range, mean and the SD of the microstrains around the implants in: comparing between MIOD assisted by four implants group I and MIOD assisted by two implants group III under bilateral vertical loading using t test, stress in group III was greater than group I, and the difference was significant. Comparing between PIOD assisted by four implants group II and PIOD assisted by two implants group IV under bilateral vertical loading using t test, stress in group IV was greater than group II, and the difference was significant. Comparing between MIOD assisted by four implants group I and PIOD assisted by four implants group II under bilateral vertical loading using t test, stress in group II was greater than group I, and the difference was significant. Comparing between MIOD assisted by two implants group III and PIOD assisted by two implants group IV under bilateral vertical loading using t test, stress in group IV was greater than group III, and the difference was significant.
|Table 1: Range, mean and SD of the microstrains around the implants in group I, II, III and IV under vertical loading|
Click here to view
[Table 2] show the range, mean and the SD of the microstrains around the implants in: comparing between MIOD assisted by four implants group I and MIOD assisted by two implants group III under bilateral oblique loading using t test, stress in group III was greater than group I, and the difference was significant. Comparing between PIOD assisted by four implants group II and PIOD assisted by two implants group IV under bilateral oblique loading using t test, stress in group IV was greater than group II, and the difference was significant. Comparing between MIOD assisted by four implants group I and PIOD assisted by four implants group II under bilateral oblique loading using t test, stress in group II was greater than group I, and the difference was not significant. Comparing between MIOD) assisted by two implants group III and PIOD assisted by two implants group I under bilateral oblique loading using t test, stress in group IV was greater than group II, and the difference was significant.
|Table 2: Range, mean and SD of the microstrains around the implants in group I, II, III and IV under oblique loading|
Click here to view
| Discussion|| |
The two models were prepared from epoxy resin material which has an appropriate elastic modulus for a bone analog material . It was also found to be better than plaster models used in other studies . Using of mucosa simulating layer from flexible polyurethane to ensure simulation of oral environment . The canine area was the site of implantation for anterior implants, resorbed maxilla show limitation of implant placement due to anatomical insufficiency especially posteriorly. This makes the canine area is the preferable for implant .
Second premolar area may be preferred for posterior implantation to avoid penetration of the maxillary sinus and consequently the need for extensive grafting . However, first molar area may be a key for implant position since the bite force doubles in a molar area when compared to the premolar area . The palate of a four implant-retained overdenture share to a lesser degree in support with inter-implant distance of 14 mm in vitro study . On the other hand the canine/premolar distribution is suggested to create hidden posterior cantilever situation which generally are believed to increase the possibility of off-axial force transmission and overloading, resulting in peri-implant–bone loss .
Installation of the strain gauges was done from the top of the models because the cervical region of the implant is the site where the highest stresses occur ,, regardless of the type of bone and the design of the implant .
Two implants in the maxilla appear to be a dental treatment alternative with increased maintenance with a few more steps in the treatment sequence for our edentulous patients . The favorable dental treatment as described by Eckert and Carr AB (four to six dental implants in the maxilla) may require extensive augmentation of the supporting structures. Many patients may not be able to proceed with an ideal plan to due to concerns related to overall health and healing capacity or simply financial resources .
In this study, a bilateral vertical static load of 100 N and oblique static load of 65 N were applied. Strain gauge studies in implantology generally use low loads varying from 20 to 300 N [36–38]. Results of this study show that there was a direct correlation between the stress distribution around implants used in the MIOD and the implant numbers, the stress increased in case of using less numbers of implants.
These results was supported by Al-Hamid et al. who proved that properly distributed four independent implants assisted maxillary overdentures associated with great amount of load reduction in comparison to others assisted by only two independent implants. Results of this study show increase the stress around the implants in case of using PIOD assisted by two implants on the contrary than using four implants.
The results of this study was explained by El-Amier et al. who stated that for PIOD retained by four implant with increasing the inter-implant distance between anterior and posterior implants is treatment of choice for patients suffering from the complete palatal coverage of the maxillary dentures.
Also supported by Al-Hamid et al. who stated that the palatal coverage may be reduced or eliminated when only properly distributed four independent implants or more are used. The worse reading was found related to the palateless overdenture assisted with two implants, this may be due to decrease in the number of implants beside the absence of palatal denture portion.
This demonstrated by Ochiai et al. demonstrated that lack of palatal coverage in a MIOD produced a greater load transfer effect and higher levels of stress concentrated around the supporting implants. Consequently, they recommended the palatal coverage for the MIOD design.
On the other hand, Sirin et al. stated that the hard palate may be source of force in denture terminals, ridges and flanges, due to fulcrum action turning the load force to compression forces in the middle and tensile forces on the denture border and alveolar ridge implant. In clinical studies on patients, El Mekawy et al. stated that using PIOD supported by two implants was considered treatment modality of choice for some patients and it is recommended as patients reported better satisfaction and more comfort.
Results of this study show increased the stress around implants in case of oblique loading of force more than the vertical loading by a significant difference. These results were supported by many researches which proved that the higher stress values of the oblique loading compared to the vertical loading, this could be attributed to the fact that the nonaxial forces tend to cause uneven stress distribution leading to areas of higher stresses and others of low stresses ,. It can be inferred that occlusal contacts positioned laterally along the axis of the implant produce higher stresses around the implant, and contribute to peri-implant–bone resorption.
| Conclusion|| |
Within the limitations of this in vitro study, it can be concluded that: removing the palatal part from MIOD could be done in case of using four implants without damaging the peri-implants tissues.
Authors contributions: S.H.M. carried out the sample preparation, measurements, data collection, and drafting of the manuscript. F.A.A.E. and M.N.E.G. participated in the conception, design, and critical revision of the manuscript for important intellectual content, All authors read and approved the final manuscript.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2]