Bio-mechanics of Dental Implant

Proceedings - 19th international Conference - iEEE/EMBS Oct. 30 - Nov. 2, 1997 Chicago, IL. USA

BIOMECHANICS OF DENTAL IMPLANT - A PHOTOELASTIC EVALUATION

ANIL KISHEN" , RADHAKRISHNAN. S. * * *Asst. Professor, Sri Balaji Dental College and Hospital, Madras, India.

**Prof. Biomedical Div., Indian Institute of Technology, Madras, India, e-mail: srk!biomed @ iitm.ernet.in.

ABSTRACT Dental biomechanics is an interdisciplinary

approach wherein engineering principles are made use of in dentistry to develop better understanding of clinical problems. In the present study photoelastic technique is utilized to compare stress distribution pattern to the supporting bone in tooth with supporting bone loss and tooth stabilized using endodontic implant. It is conclusive that endodontic implant in tooth with supporting bone loss can induce deleterious effects on the supporting bone.

Keywords: Endodontic implant, Photoelasticity, stress distribution, Supporting Bone loss, stress concentration.

INTRODUCTION Endodontic implant is a type of dental implant

where a rigid metallic structure is fixed through the root canal of the tooth into the bone, as a treatment methodology for tooth with altered crown root ratio [ 11. They can be used effectively to improve the prognosis of a mobile tooth due to trauma or pathological loss of tooth structure or bone support.

Endodontic Implants are unique when compared to other dental implant system in that

(a) they are not exposed to the oral cavity (b) their dimensions being very small, the area of bone to

be prepared to receive the implant is not extensive (c) the angulation of the implant is easily established

through the root canal. Inspite of these advantages the endodontic implant has not been widely practiced [2]. Recent trends has been to apply physical principles and Engineering techniques to study the behaviour of the biological structures [3]. Biomechanical studies in dentistry gives a better understanding of dental structures under functional forces [4]. In the present study photoelastic experiments are conducted to study the stress distribution pattem in tooth with endodontic implant with supporting bone loss and a comparison with a non implap pathological condition is made.

MATERIALS AND METHODS The photoelastic stress analysis is based on the

principle of double refraction (Bire fringence) of some transparent materials. When loaded these materials exhibit interference fringes when viewed with a polarised light.

These fringe patterns produced under an external force represent the distribution of internal stresses within the complex structure under load. There are two groups of fringe patterns identified. These are isoclinics and isochromatics which gives information about the direction and magnitude of principle stress respectively.

In the present study, models for the stress analysis were prepared using Epoxy resin (Araldite Y230 & HY95 1). The resin and hardner were taken in separate containers, heated in an oven at 90C for 3 hrs. After cooling, it was mixed carefully in the proportion of 100:8 (Resin : Hardner) by weight and poured into a perspex mould and two tooth models for use in the study were made.

Model 1 The model 1, simulates weakened tooth with

supporting bone loss. This model had crown root ratio different from the normal.

Model 2 The model 2 was used to study stress distribution

pattem in tooth and supporting bone after stabilization with endodontic implant. This model had a smooth parallel sided stainless steel implant placed through the tooth into the bone.

The experimental set up consisted of :

1. Light source 2. Polariscope 3. Model 4. Video Camera 5. Digital image processing system

In this experiment each model was mounted on an aluminum frame work between the first quarter wave plate and second quarter wave plate of the polariscope. A monochromatic light was passed through it. The specimens were loaded with 112 N, 157 N and 225 N forces in three directions which are vertically along the long axis of the tooth, at 30" and at 60' lingual to the long axis of the tooth. The digital image processing system was used for the analysis of the fringes thus obtained. RESULTS

The stress distribution pattems obtained by photoelastic experiments were analysed and compared for the following two cases.

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Proceedings - 19th International Conference - IEEE/EMBS Oct. 30 - Nov. 2, 1997 Chicago, IL. USA

a. Tooth weakened with supporting bone loss b. Tooth with endodontic implant

The results obtained from the digital image processing system for the following cases are as follows.

I. For fringe pattem representing stress distribution in tooth weakened with supporting bone loss. (refer Fig. IA, 1B)

i. It is seen from the fringes that the Stress on the supporting bone increases with the lingual inclination of bite force from vertical direction.

ii. Stresses are higher along the labial side than on the lingual side of the tooth and supporting alveolar bone

iii. Stress are zero near the root apex iv. Stresses are found concentrated at the region of

defective supporting bone where the stress are pathogenic.

11. For Fringe pattems representing stress distribution in tooth with endodontic implant the results indicate that the (refer Fig.2A,2B).

i. Fringe pattems vary with the direction of occlusal force with the maximum being on the lingual side when compared to labial side.

ii. Stresses concentrate more near the root apex, making it a highly stressed region.

DISCUSSION

A crucial factor affecting the longevity of implant is the nature and degree of force acting on the implant. The endodontic implant also known as endodontic stabilizer receives occlusal stress from the tooth during function. These stresses are of significance for the better prognosis of the implant.

In the first experimental study, the stress distribution pattem in a tooth weakened due to periodontal pathosis simulating supporting bone loss was investigated. It was observed that stresses were concentrated in the regions of bone loss. It was further noted that stress in the supporting bone was higher on the labial surface when compared to the lingual surface.

In the second experimental model with the endodontic implant it was found that the stresses were higher in the lingual aspect when compared with the labial aspect. The reason for the shift of higher stress pattem may be due to the presence of endodontic implant, which may be the contributing factor to the leverage in the stabilized teeth. In our investigation distinct stress concentration was observed at the root apex in the model with endodontic

implant which is in confirmation with the previous researchers. Excessive movement of the stabilizer may induce stresses with deleterious effect in the apical region of the root. This can be minimised by using a,stabilizer system that may provide a suitable match between the endodontic implant and the prepared channel.

From the foregoing analysis and discussion it is evident that endodontic endosseous implant may be thought of in certain clinical situations such as inadequate root length, tooth with horizontal root fracture, in cases with severe intemal resorption and in apicoectomy, where large portion of root is lost with healthy supporting structures. On the contrary, Endodontic implant should be avoided in tooth with severe bone loss.

SUMMARY AND CONCLUSION

Photoelastic experiments were conducted to study the stress distribution pattem in models simulating clinical conditions of a tooth weakened with periodontal pathosis and stabilized with endodontic implant.

In models simulating supporting bone loss due to periodontal pathosis, stress concentration was observed in the region of defective alveolar bone. .The tooth with endodontic implant showed more stress on the lingual side of the supporting bone compared to the non-implant model.

From the above study it can be concluded that with proper case selection and ideal configuration of endodontic implant one can achieve better prognosis and success in clinical practice.

REFERENCE

1. Alfred C.Frank, Endodontic Endosseous Implant and treatment of wide open apex. Dental clinics of North America, 675-690. Nov. 1967.

2. Deines D.N. Eick J.D., Cobb C.M., Bowles C.Q. and Johnson C.M., Photoelastic stress analysis of natural teeth and three osseointegrated implant designs. 1nt.J.Periodontics Restorative Dent., 13(6), 540-549, 1993.

3. Franklin S.Weine and Alfred L.Frank, Survival of the endodontic endosseous implant. J. of Endodontics, Vo1.19( 10) : 524-531, Oct. 1993.

4. Mahler and Peyton, Photoelasticity as a research technique for analysing stresses in dental structures. J.Dent.Res.. 34, 831- 838. 1955.

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Direction of force

lingual side labial side

Supporting bone

Fig.lA Model 1 - Isoclinic fringe patterns for different occlusal forces and direction

Fig. 1B Model 1 - Isochromatic fringe pattems for different occlusal forces and- direction

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Fig.2A Model 2 - Isoclinic fringe patterns for different occlusal forces and direction

Fig.2B Model 2 - Isochromatic fringe pa t tems for different occlusal forces and direction

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