Bangalore 3. Course of the study and the subject Master of Dental Surgery (MDS)
Prosthodontics 4. Date of admission to the course
10-06-2012 5. Title of the topic
Bone implant contact and its relationship with the strain
in the surrounding bone
6. Brief resume of the intended work 6.1 Need for the study
Success of dental implant treatment depends on the bone implant contact and the prognosis depends on the strain developed in the surrounding bone when the implant is loaded. Sixty percent of the implant surface should have bone contact to ensure successful load transmission, and to limit the strain values between 50-1500 microstrain which falls in the adapted window. However, the area of bone implant contact and the strain generated have not been correlated. This study is undertaken to find out the possible relationship between different degrees of bone implant contact and the corresponding strains generated in the surrounding bone.
Seong W J, Korioth T and Hodges J studied the effect of implant design, load location, direction and magnitude of axial and bending (buccolingual and mesiodistal) strains on three different implant designs. The implant designs used were single, 3.75mm (regular) diameter implant, single 5mm (wide) diameter implant, two, 3.75mm implant connected through a single molar crown. Three identical models with missing first molar were duplicated in acrylic. The selected implants were inserted perpendicular to the occlusal plane into the buccolingual center of the alveolar crest. Metal crowns were fabricated over the implant abutments. Strain gauges were attached to the casting. Models with single implant had 4 strain gauges and model with 2 implants received 8 strain gauges. A tensile testing machine was used to apply loads of 35 and 70 N on the occlusal surface of each casting. 0 degree and 15 degree off-axis buccolingual forces were applied at 3 different occlusal locations viz. the central fossa, the distal marginal ridge, and the distobuccal cusp tip in the same plane. The results showed that, for buccolingual bending and axial strains, implant design with two implants experienced the least strain (3160 µƐ) followed by a larger diameter implant and regular implant. For mesiodistal bending strain, larger diameter implant experienced the least strain (3958 µƐ), and, the two implant design connected by a single molar crown experienced the maximum mesiodistal bending strain (6493 µƐ). When loads were applied at different locations, distobuccal cusp tip induced the largest bending strains in the buccolingual plane, whereas, distal marginal ridge created the largest bending strain in the mesiodistal plane. On testing the main effect of direction, 15 degree off axis buccolingual force induced more strain than a 0 degree force for buccolingual bending strains. Results on testing the main effect of magnitude, showed that when the magnitude of force was doubled from 35 to 70 N the strain increased in all the plane for all the designs. It was concluded that for single-molar implant designs, an increase in implant number and diameter may effectively reduce experimental implant abutment strains.
Ishigaki S,Nakano T, Yamada S, Nakamura T, and Takashima Fstudied the biomechanical stress distribution in supporting bone around an implant and a natural tooth under chewing function. A three dimensional finite element model of mandibular first molar and titanium implant of 4 mm diameter and 10 mm length were constructed. Antagonist maxillary molars were also constructed as an opponent during chewing function. A gap of 0.5mm was given between the two teeth to provide space for the food material. To determine the magnitude of chewing force, 20 adult volunteers with no missing teeth and no signs of TMJ disorders were selected. Among them 10 volunteers were selected with grinding type chewing pattern and 10 volunteers were selected with chopping type of chewing pattern. An average of 10 chewing cycles after 5 seconds of mastication on the left and right side were analyzed and the magnitude of chewing force was selected as 200 N. The result showed that the natural tooth model showed smooth stress distribution in the supporting bone in both the mesiodistal and the buccolingual directions except at furcated area wherein compressive stress was found. Conversely, the implant model showed stress concentration in the supporting bone around the neck of the implant especially in the buccal area. The grinding type model of implant showed higher tensile stress concentration than the chopping type at the lingual neck of the implant. Thus it was concluded that the natural tooth model showed smooth stress distribution in supporting bone, while the implant model showed high stress concentration in supporting bone around the neck of the implant.
Hekimoglu C, Anıl N, and Cehreli M C compared the strain around a natural tooth opposing an implant with the strain around the occluding implants that were subjected to static and dynamic loads. Acrylic models of both the jaws were fabricated which were mounted on a semi adjustable articulator. In the models, mandibular and maxillary first molars were trimmed. On one side, implants were placed both on the upper and the lower jaw. On the contralateral side, a natural extracted mandibular molar was integrated into the model, which opposed an implant. Before placing the natural tooth on the model, a vinyl polysiloxane adhesive was painted on the roots of the natural extracted tooth and allowed to dry for 5 minutes, to simulate periodontal ligament. Metal ceramic crowns were placed on the implants and also on the natural tooth opposing implant. Strain gauges were attached on the neck of implant and on the buccal surface of the natural tooth. The specimens were then fixed on the base of a programmable pneumatic loading machine, and strain under 75N and 100N of static axial and dynamic lateral loads were measured. The result showed that compressive strains were induced around natural tooth and implants as a result of static loading, whereas combinations of compressive and tensile strains were observed during lateral dynamic loading. Strains around the natural tooth were significantly lower (9-146µƐ) than the opposing implant (30-292 µƐ) and occluding implants (24-236 µƐ) in the contralateral side. The highest strain generation around natural tooth (146 µƐ), and all implants were induced in the midbuccal region as compared to mesial and distal surface. Among the implants the highest strain of 292 µƐ was found at the midbuccal region of opposing implants. The mean strain level around the implant opposing a natural tooth (30-263 µƐ) was lower as compared to occluding implants (54-230 µƐ) of the contralateral side on static loading, but during dynamic loading the implant opposing the natural tooth showed higher strain value of (292 µƐ) as compared to occluding implants. Thus, it was concluded that strain magnitudes around occluding implants experienced similar strain as an implant occluding a natural tooth, although there was a general tendency for the implant opposing the natural tooth to experience higher strains under dynamic lateral loading.
Bozkaya D, Muftu S and Muftu A investigated the effects of external geometry and occlusal load magnitude on bone failure for five commercially available dental implant systems namely Ankylos, Astra, Bicon, ITI, and Nobel Biocare. These implant systems were comparable in size, but different in thread profile and crest module shapes. The crestal modules of Ankylos and Bicon systems had narrow cross sections, and the other 3 implants had wide cross sections. Finite element analysis was used for this study. Implant to bone contact was assumed to be 100%. Occlusal loads of varying magnitudes (0 to 2000 N) were applied on the abutments supporting single tooth restorations at 11.3 degrees from the vertical axis. Forces from different directions were applied, from vertical direction, lateral, bending and occlusal. From the results it was found that occlusal load, does not cause large overloaded regions up to load magnitudes of 1000 to 1200 N. The bone failure area due to overloading was found to be highest for ITI system of implants (0.205 mm2-0.305 mm2) and lowest for Ankylos implant system (0 mm2-0.134 mm2). Near the superior region of the compact bone, no overload was observed for the Ankylos and Bicon systems; however, overload regions in compression were found for Astra, ITI, and Nobel Biocare systems. All of the implants eventually developed maximum tensile stresses above 100 MPa at the intersection of trabecular bone, cortical bone, and implant due to high occlusal loads. In this region, Ankylos implant developed the least amount of overload area followed by Nobel- Biocare, Bicon, and Astra with comparable values; the ITI system showed the largest overload area. Thus it was concluded that at the extreme end of the occlusal load range (1000 N or more), for example, simulated parafunction, the overloading characteristics of different implant systems were dependent upon shape of the crestal module of the implant. In general, overloading occurred near the superior region of the compact bone, in compression, and was primarily caused by the normal and lateral components of the occlusal load. At the intersection region of the compact and trabecular bones, overloading occurred in tension and was primarily due to the vertical component of the occlusal load.
The following review can be referred to the text book of contemporary implant dentistry by Misch CE and Abbas HA. Bidez MW, Misch CE said that greater the magnitude of stress applied, more strain is observed in the bone. Bone modeling and remodeling are controlled partly or entirely by the mechanical environment of strain. Frost HM proposed four histological patterns in bone viz. pathological overload window, mild overload window, adapted window and acute disuse atrophy window in relation to the amount of microstrain observed. Disuse atrophy is seen in the microstrain levels ranging from 0-50 units. Bone in acute disuse atrophy loses mineral because modeling for new bone is inhibited and remodeling is stimulated with a gradual loss of bone. Adapted window ranges from 50-1500 units, it represents an equilibrium of modeling and remodeling. The bone formed in adapted window is lamellar. Microstrain levels ranging from 1500-3000 units results in mild overload. Mild overload causes a greater rate of fatigue micro fracture and increase in cellular turnover rate of bone. As a result bone strength and density decreases. This is a condition of overload, thus, in an attempt to change the strain environment, woven bone is formed, that is less mineralized than the mature lamellar bone. When the strain levels are further increased to greater than 3000 units, pathological overload causes bone loss that eventually results in implant failure. Cortical bone fracture has been reported at microstrain levels of 10000 to 20000 units.
Morita Y, Qian L, Todo M, Matushita Y and Arakawa K made use of digital image correlation method to measure strain that was developed around cortical/cancellous bone models when the implants were loaded under compressive loads using a universal testing machine. Bilayer bone model of dimension 40x40x30 mm³ were fabricated using glass reinforced epoxy and solid polyurethane resin. Implants of dimensions 4.7mm diameter and 16mm long were placed on the bone model. The specimens were cut in cross-sections to observe the fixture/bone interface. A synthetic resin pigment and organic solvent was sprayed on the area to be observed for Digital Image Correlation analysis (DIC). A compression load was applied till it reached the value of 400N, at a cross head speed of 0.5mm/min. The load and displacement were recorded throughout the loading. Digital images of the specimens surface were taken every 10N during continuous loading. The results showed that at a load of 400N the displacement was 0.86 mm and displacement increased linearly with increase in load. The DIC results indicated that the deformation was concentrated at the fixture/bone model interface and that the deformation distribution became discontinuous at the cortical and cancellous bone boundary. Strain distributions calculated from the displacement distributions, showed maximum strain was concentrated in the bone near the tapered portion of the implant (1.7% and -4.2%), and the cortical cancellous interface along the lower end of the implant (-11%). Thus it was concluded that in immediate loaded implants the strain is concentrated at the tapered end of the implant, lower end of the implant and the interface between the cortical and cancellous bone.
Heidari B,Bisadi H, Heidari B and Kadkhodazadeh M determined the effect of cylindrical and tapered implants with different degree of tapering and similar lengths on the stress and strain distribution in the bone and implant using finite element analysis. One cylindrical and five types of tapered implants with degree of tapering of 0.02, 0.06, 01, 0.12 and 0.16 were modelled with computer software. The bone model comprising of compact and spongy bone was made for the implant placement. A pressure of 30 psi, which is close to normal occlusal pressure, was applied axially on lower edge of the abutment. The results from stress/strain distribution in bone showed that with increased degree of implant tapering, the stress and strain increased in the bone. In all types of implants, maximum stress occurred in a region of cortical bone adjacent to implant neck and lower bound of cortical bone. Maximum stress was seen in apex of implant in spongious bone. The highest maximum stress of 0.572 MPa and maximum strain of 0.11 x 10-3 was observed in bone with implant with a taper of 0.16. The lowest maximum stress of 0.466 MPa and maximum strain of 0.881 x 10-4 was observed in bone with cylindrical implant. Stress/strain distribution in implant showed that in all types of implants maximum stress and strain was generated at the abutment-implant interface. The lowest maximum stress of 1.46MPa was generated in implant with a taper of 0.02 and highest maximum stress of 2.3MPa was generated in implant with 0.12 taper. It was also noted that as the taper of the implant increased the stress concentration decreased from 0.58 MPA to 0.25 MPa at the neck of the implant in the region between cortical bone and abutment. The lowest maximum strain of 0.129x10-4 was generated in implant of 0.06 taper and highest was generated in implant with 0.12 taper which was 0.201x10-4. It can be concluded from the study that the cylindrical screw implant without any degree of taper generated the lowest maximum stress in cortical bone and implant with highest taper degree generated the highest maximum stress.
Djebbar N, Serier B, Bouiadjra B B, Benbarek S, and Drai A evaluated the effects of external loading on the stress distribution in the dental implant with finite element analysis. A three dimensional bone model was constructed composed of spongy centre surrounded by 2 mm of cortical bone. Screw form implant of diameter 4.1 mm and length of 14 mm were placed in the bone model. The abutment placed were 7.2 mm long with lower diameter of 2.6 mm and the upper diameter of 3.6 mm. The implants were loaded three dimensionally, with forces of 17.1 N, 114.6 N and 23.4 N in a lingual, an axial and a mesio-distal direction. The stress distributed in abutment, implant, bone and the bone-implant interface were evaluated. The results showed that the stress distribution in abutment was concentrated at the interface between the abutment and the implant and at the fixing part of the abutment when load was applied in mesiodistal direction. Axial loading of the implants produced stress level that was concentrated at lower part of the implant. Mesiodistal loading of implants showed stress concentrated at the upper part and proximal zone of the implant. The stress level in the bone was highest at the side part of the bone in its proximal zone when the implants were loaded axially and mesiodistally. Stress distribution along the bone implant interface was highest at the upper contact zone between the bone and the implant which was found to be greater than 80 MPa on loading of implants mesiodistally. Thus it was concluded that stress induced on the elements of the dental prosthesis depend on the nature of the mechanical load applied and mesiodistal loading of implants produce high stress in bone and implant that can be fatal for the structure of the implant and the patient.
Rungsiyakull P et al studied the effect of occlusal design on the strain development in simulated bone by using triaxial strain gauges attached to the cervical region of each implant. Occlusal design, load location and magnitude were examined to determine the maximum axial principal strains of four occlusal designs viz. 30˚ cusp inclination and 10˚ cusp inclination with 4 and 6 mm occlusal table dimension. Acrylic was used to simulate bone, in which implants were embedded with different implant and occlusal configurations. Strain gauges were attached to the buccal and the lingual cervical region of the specimens. The forces were applied on the central fossa and on a point 2 mm buccal to the central fossa. Universal testing machine was used to apply load. Static load in the range of 50, 100, 150, 200 and 250 N was applied for a period on 15 seconds on both the sites. The result showed that the implant with 30˚ cuspal inclination and occlusal table dimension of 6 mm showed the maximum strain developed around the surrounding bone (1259.9 µstrain), whereas it was lowest for 10˚ cuspal inclination with 4mm occlusal table dimension (5.1 µstrain). Thus it was concluded that a reduced cusp inclination and occlusal table dimension effectively reduced bone strain on implant-supported single crown. The occlusal table dimension appeared to have a relatively more important role than cusp inclination.
El-Anwar M, El-Zawahry M and El-Mofty M studied stress distributions and displacements of threaded dental implant designs of different diameter and length and their effect on cortical and spongy bone. Using finite element analysis, twenty-five different implant designs with gradual increase in diameter ranging from 3.5 – 6 mm and length ranging from 9 – 13 mm were made. Each implant model was subjected to four different loading conditions viz. tension of 50N, compression of 100N, bending of 20N and torque of 2Nm. Load was applied on the top middle node of each implant assembly in the study model. Torque was generated by using two equal forces in magnitude, opposite in direction, applied to two opposite points on the implant head. Linear static analysis was performed. Result showed that, increasing implant length from 9 to 13.3 mm can improve its behaviour by reducing stresses generated on both types of bone by 20-30%. On the other hand increasing the implant diameter from 3.5 to 6mm reduces such stresses by 30-50%. Increasing implant diameter has dominant effect over increasing the implant length. Thus it was concluded that increasing implant diameter and length generates better stress distribution on spongy and cortical bone.
To measure the strain developed in the simulated bone around implants with different percentages of bone implant contact viz. 50%, 75% and 100%.
7. Materials and methods
Implant replicas (MIS, Israel)
Implant abutments (MIS, Israel)
Auto-polymerizing acrylic resin (DPI, Mumbai)
Interim restorative material (Dentsply, USA)
Strain gauge (350 Ω, gauge factor 2.01)
Strain gauge indicator
Universal testing machine (Nano plug and play - ISN 67)
Preparation of specimen :
Thirty implant analogue of dimension 3.75 X 11.5 mm will be mounted in a simulated bone model of auto-polymerizing polymethylmethacylate blocks measuring 1” X 1” X 1” with bone implant contact of 100%, 75%, and 50% . The difference in the bone implant contacts will be created by the use of modelling wax. To simulate 50% bone implant contact, 50% of implant surface will be covered with wax, similarly, about 25% of the implant surface will be covered with wax and embedded in acrylic to simulate 75% bone contact. The 100% bone implant contact will be achieved by completely embedding the implant in acrylic resin block. The wax used for covering the implant surface will be eliminated by injecting hot water through a sprue created in the resin blocks. The sprue will be made by incorporating 19 gauge wire during the mould preparation of the acrylic block. Radiographs of the prepared acrylic blocks were taken to ensure different bone implant contacts. In order to make the acrylic radiopaque, barium chloride (5%) will be added in the acrylic powder. The implant abutments will be connected to the embedded implant on which metal ceramic crown will be cemented. Strain gauges will be bonded on the prepared specimen, adjacent to the cervical area of each implant on the buccal and the lingual side. For bonding of the strain gauges, the dimensions of the specimens will be first standardized using a digital vernier caliper. The surfaces of the specimen will be made flat and polished properly for correct bonding of the strain gauges. The prepared surface will be cleaned using isopropyl alcohol and then the strain gauges will be bonded on the specimen using cyanoacrylate. The bonded strain gauges will be soldered to the terminal using a silver solder. The prepared specimen will then be connected to a digital strain gauge indicator. Static loads of 200, 400, 600, 800 N will be applied at the central fossa of the metal ceramic crown using a universal testing machine (Nano plug and play-ISN 67) using a stylus of 0.8 mm diameter. The strain developed will be measured in the digital strain gauge indicator connected to the specimen.
Fig.1 Schematic representation of the specimen Statistical analysis
The results obtained will be subjected to factorial ANOVA.
Methodology Implant analogues and abutments
Load application at central fossa
Bonding of the strain gauges
Cementation of metal ceramic crown
Mounting of implant analogues with 50%, 75%, and 100% bone implant contact
8.1 Does the study require any investigations or interventions to be conducted on patients or other humans or animals?
8.2 Has ethical clearance been obtained from your institute?
8.3 Trial test done if any?
9. Signature of the candidate
10. Remarks of the guide: The study is related to implant treatment prognostication.
11. Name and designation of -
11.1 Guide – Dr. Divya Hegde, Professor of Prosthodontics
11.3 Co- Guide if any - Dr. Lakshmikanth, Asst. Professor of Prosthodontics
11.5 Head of the department - Dr. K Chandrasekharan Nair
12.1 Remarks of the principal
List of references :
Seong W J, Korioth T, Hodges J, Experimentally induced abutment strains in three types of single-molar implant restorations, J Prosthet Dent 2000
Ishigaki S,Nakano T, Yamada S, Nakamura T, Takashima F, Biomechanical stress in bone surrounding an implant under simulated chewing Clin. Oral Impl. Res 2003:14;97–102
Hekimoglu C, Anıl N, Cehreli M, Analysis of strain around endosseous dental implants opposing natural teeth or implants, J Prosthet Dent 2004;92:441-6
Bozkaya D, Muftu S, Ali Muftu A, Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite elements analysis, J Prosthet Dent 2004;92:523-30
Misch CE, Abbas HA, contemporary implant dentistry, 3rd edition, Missouri, Elsevier 2008, pp 132-134
Morita Qian L, Todo M, Matushita Y, Arakawa K, Strain Distribution around Dental Implants in Cortical/Cancellous Bone Models using DIC Method Yasuyuki: Proceedings of the SEM Annual Conference June 1-4, 2009 Albuquerque New Mexico USA
Heidari B,Bisadi H, Heidari B, Kadkhodazadeh M, Influence of Different Tapered Implants on Stress and Strain distribution in Bone and Implant: A Finite Element Analysis J Periodontol Implant Dent 2009e2; 1(1):11-19
Djebbar N, Serier B, Bouiadjra B, Benbarek S, Drai A. Analysis of the effect of load direction on the stress distribution in dental implant. J Mater Design 2009
Top Rungsiyakull P, Rungsiyakull C, Appleyard R, Swain M, Klineberg I Loading of a single implant in simulated bone, Int J Prosthodont 2011;24:140-143
El-Anwar M, El-Zawahry M, El-Mofty M, Load Transfer on Dental Implants and Surrounding Bones, Australian Journal of Basic and Applied Sciences 2012; 6(3): 551-560