BIOMAT., MED. DEV., ART. ORG., 7(1), 105-110 (1979)

STRESS ANALYSIS OF SINGLE-TOOTH IPPLANTS 11. EFFECT OF IIIPINI ROOT-LENGTH VARIATION AND

PSElJD3 PERIODONTAL LICJ\FIENT INCORPORATION

G. H. Atmaram, Ph.D., and Hamdi Mohammed, D.D.S., M.Sc.D., Ph.D. Department of Dental Biomaterials

College of Dentistry, University of Florida Gainesville, Florida 32610

ABSTRACT This study delineates the effects of varying the root length as well

as incorporating a soft pseudo periodontal ligament on the overall stress distribution for each of five different implant materials and one implant design .

Introduction

Previous investigations on ankylosed single-tooth implants of normal

root length have shown that a cylindrical implant root geometry results

in more favorable stress-distribution than a conical or a natural-tooth

root configuration'".

further optimize the biomechanical design of cylindrical implant by in-

vestigating the effect of two additional modifications in the root design:

(i) increasing the root length of the ankylosed implant and (ii) incorpor-

ating a soft liner to simulate a pseudo periodontal ligament at the implant-

alveolus interface.

The present study was undertaken in an attempt to

Materials and Methods

The method of finite element analysis (FEA) was used to obtain the

stress values in the models of tooth implant and their supporting tissues.

The implant with a cylindrical root geometry was selected for all the

models, since it generated more favorable stress distribution than both

10 5

Copyright 0 1979 by Marcel Dekker, Inc. All Rights Reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any informationstorageand retrievalsystem, without permission in writing from the publisher.

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106 ATMARAM AND MOHAMMED

the conical and natural-tooth configurations'' '. The three configurational

variations of the cylindriGa1 implant investigated are depicted i n figure

1. For each configuration the mesiodistal section of 1 nun thick slice

centrally located in the buccolingual direction of the tooth was selected

for the analysis as a plane stress model.

dontal ligament, the thickness of this ligament was simulated to be 1 mm.

The simulated load on each model was equivalent to the load of 45 kgms

evenly distributed over the occlusal surface of 0.82 cm .

For implants with pseudo perio-

2

The alveolar region in all models was described by the elastic para-

The pseudo periodontal ligament, when con- 2 meters of the cortical bone . sidered, was represented by modulus of elasticity - E = 700 Kgm/cm ,

Poisson's ration - v = 0.45 and shear modulus - G = 241 Kgm/cm . configuration illustrated in figure 1, five different implant materials

with a wide variation in their elastic parameters were successively

simulated for the implant region.

vitallium, titanium, dentin, vitreous carbon and PbNA. The elastic para-

2

For each 2

These five implant materials were:

L meters of these materials were described previously . are considered to be homogenous, isotropic and within their elastic limit

when loaded.

A l l the materials

NORMAL ROOT LENGTH ANKYLDSED IMPLANT IMPLANT WITH ANKYLOSED IMPLANT LONGER ROOT LENGTH PSEUDO P D L -

NORMAL ROOT LENGTH

FIG. 1. Configurational Variations of Cylindrical Implants.

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SINGLE-TOOTH LMPLANTS. I1 10 7

Results and DiscussjE

Each FEA simulation pertaining to a particular design combination

describes stress components ux (lateral), u

(shear) for each element of the model.

tions simulated, longitudinal stresses were predominant and were found

to be compressive in nature.

stress in the implant and alveolar region for each design variation are

given in tables I and 11, respectively.

efficacy of each of the fifteen designs studied. Also indicated in

table IIare the maximum values of longitudinal stress in the pseudo

periodontal ligament for the respective five designs.

(longitudinal) and T Y X y

For the occlusal loading condi-

The maximum values of the longitudinal

The tables illustrate the overall

Except for PhIMA implants, providing the longer implant root

generally results in

implant and the alveolus.

insignificant reduction of maximum stresses both in the

When the implant material has either high (vitallium, titanium) or

low (PkMA) elastic modulus in comparison to that of the alveolar bone, the

TABLE 1

Maximum Values of Longitudinal Compressive Stresses in the Implant Region for Different Design Variations (Kgm/cni 1

- Material Vitallium Vitreous

Configuration Dentin (Cast) Titanium Carbon P h B E

Ankylosed Im- plant-Normal 62 59 59 62 67 Root Length

Ankylosed Im- plant-Longer 62 5s 59 62 67 Root Length

Implant with Pseudo PDL- Normal Root Length

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108 ATMARAM AND MOHAMMED

TABLE I1

Maximum Values of Longitudinal Compressive Stresses in the Alveolar Bone for Different Design Variations (Kgm/cm )

Mat er i a1 Vitallium Vitreous

Configuration Dentin (Cast) Titanium Carbon PPlMA

Ankylosed Im- Dlant-Normal 26 37 37 28 42 koot Length

Ankylosed Im-

Root Length plant-Longer 25 37 35 26 33

Implant with Pseudo PDL- 31 32 32 31 30 Normal Root 32(in PDL) 33(in PDL) 33(in PDL) 32(in PDL) 31(in PDL) Length

placement of the pseudo periodontal ligament reduces the large alveolar

stresses significantly. Using these materials, the ankylosed implants are

characterized by a high degree of elastic mismatch at the implant-alveolus

interface,which potentiates high stress concentrations. Hence, the soft

pseudo periodontal ligament acts as a stress transfer layer transmitting

load from the implant to the bone uniformly and thereby reducing high

stress concentrations. 1,3 . This result is in agreement with previous studies

When the implant material has a modulus close to that of the alveolar

bone (dentin and vitreous carbon), the incorporation of the pseudo perio-

dontal ligament decreased the high implant stresses, but increased the

high alveolar stresses (figure 2 ) . Since the primary consideration in

biomechanical optimization of tooth implant design is to reduce high

alveolar stresses, the incorporation of the pseudo periodontal liagment,

when the modulus of the implant material is close to that of bone, is not

advantageous.

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SINGLE-TOOTH IMPLANTS. I1 109

LEGEND 0 0-15 k g m / c m '

15-30 k g r n / c m 2 30-60 kgrn/Cm2 60-90 kgrn/cm2

FIG. 2a. Distribution of Longitudinal Compressive Stresses for Ankylosed Implant with Elastic Parameters of Vitreous Carbon/Dentin.

LEGEND 0 0-15 k g m l c m 2

0 3 0 - 6 0 kgm/cm2 1 5 - 3 0 k g m / c m 2

1 .\\\\,-,,,-

FIG. 2b. Distribution of Longitudinal Compressive Stresses for Implant with Pseudo PDL. Implant Has Elastic Parameters of Any of Five Materials.

When the five designs incorporating pseudo periodontal ligaments are

compared, it is interesting to note that the maximum stress values in

the implant, in the pseudo periodontal ligament and in the alveolar bone

are nearly equal and independent of the implant material, as depicted in

tables I and 11. Further, the overall stress distributions (figure 2b)

also become independent of the implant material. In this situation, the

pseudo periodontal ligament alone dictates the biomechanics of the tooth

implant, irrespective of the implant material employed. Art

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110 ATMARAM AND MOHAMMED

Conclusions

The results discussed above lead to the following conclusions:

1. Providing longer than normal root length for a cylindrical

implant offers a significant reduction in high alveolar stress only if

the implant material has a relatively low elastic modulus in comparison

to that of the alveolar bone.

2 . While the incorporation of the pseudo periodontal ligament at

the implant-bone interface generates more favorable stress distribution

for implant materials with significantly higher or lower modulus of

elasticity than that of the alveolar bone, the placement of such a

ligament does not have similar beneficial effect for implant materials

with elastic modulus close to that of the alveolar bone.

3 . When a pseudo periodontal ligament is used, it alone dictates

the resulting stress distribution, irrespective of the implant material

employed, provided that the pseudo periodontal ligament is considerably

softer than both the implant and the bone.

1.

2 .

3 .

References

H. Mohammed, G. H, Atmaram, and F. J. Schoen: Analysis of Single Tooth Implants with Different Root Configura- tions, Trans. SOC. Biomat. ___ i:71, New Orleans, Louisiana, (April, 1977).

G. H. Atmaram, H. Mohammed, and F. J. Schoen: Stress Analysis of Single Tooth Implants. I. Effect of Elastic Parameters and Geometry of Implant, Trans. Int. Symp. Rioniat. Dent. & Pled., Los Angeles, CA (Dec. 1976).

J. D. Buch, J. G. Crose, and C. D. Bechtol: Biomechanical and Bio- material Considerations of Natural Teeth, Tooth Replacements and Skeletal Fixation, J. Biomat. Med. Devices Art. Organs 2:171-186 (1974).

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Photoelastic Stress

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