MODIFIED POLYALKENOATE CEMENTS FOR DENTAL APPLICATIONS

Transcription

1 MODIFIED POLYALKENOATE CEMENTS FOR DENTAL APPLICATIONS by D.V.S. MURTHY A thesis submitted to the Indian Institute of Technology, New Delhi for the award of the degree of DOCTOR OF PHILOSOPHY INDUSTRIAL TRIBOLOGY MACHINE DYNAMICS AND MAINTENANCE ENGINEERING CENTRE INDIAN INSTITUTE OF TECHNOLOGY, DELHI June 1994

2 _to my parents

3 CERTIFICATE This is to certify that the thesis entitled, "Modified Polyalkenoate Cements for Dental Applications" being submitted by Mr.D.V.S.Murthy to the Indian Institute of Technology, Delhi, for the award of the degree of Doctor of Philosophy, is a record of bonafidd research work carried out by him. Mr.Murthy has worked under our guidance and supervision and has fulfilled the requirements which to our knowledge have reached the requisite standard for the submission of the thesis. The results contained in this thesis have not been submitted in part or full to any ether University or Institute for the award of any degree or diploma. Raj K.Bansal Parkash Singh U.S.Tewari Thesis Thesis Thesis Co-Supervisor Co-Supervisor Supervisor

4 ACKNOWLEDGEMENTS I am highly grateful to Dr. Raj K. Bansal, Associate Professor, Department of Chemistry, Indian Institute of Technology, Delhi; Dr.Parkash Singh, Chief, Biomaterials, Shriram Institute for Industrial Research, Delhi and Dr.U.S.Tewari, Senior Design Engineer, Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC), Indian Institute of Technology, Delhi for their invaluable guidance, encouragement, co-operation and constructive criticism during the course of this work. I take this opportunity to express my deep sense of gratitude to Dr.D.A.Dabolkar, Joint Director and Dr.J.K.Nigam, Director, Shriram Institute for Industrial Research, Delhi for constant encouragement and assistance at various stages without which the present work would not have been possible. I also express my sincere thanks to the management of the Shriram Institute for granting permission to do Ph.D and also providing the facilities to carry out the work successfully. Thanks are also due to all my colleagues at Shriram Institute for the help rendered during the course of the work. I am grateful to the authorities of Indian Council of Medical Research (ICMR) for sponsoring the project at Shriram Institute under which some part of the present work has been carried out.

5 Thanks are also due to Dr.Braham Prakash, Senior Design Engineer and technicians of ITMMEC, Indian Institute of Technology, Delhi for their assistance for carrying out the wear studies successfully. Assistance rendered by Dr. G.Bose of CARE, Dr.Chattar Singh of ITMMEC, Indian Institute of Technology, Delhi for the Scanning Electron Microscopic (SEM) analysis gratefully acknowledged. A debt of gratitude to my wife Bharathi for her inspiration and constant encouragement. Lastly I wish to express my appreciation to Mr.R.S.Mahto for his patience and excellent typing. (D.V.S.MURTHY)

6 ABSTRACT TOPIC : Modified Polyalkenoate Cements for Dental Applications The thesis is divided into three chapters namely Introduction, Experimental and Results and Discussion. In the first chapter a general introduction of literature on the dental cements has been reviewed. Historical development of dental cements including the evolution of dental cements such as zinc phosphate, silicate, silicophosphate, zinc oxide eugenol, polycarboxylate, glass-ionomer and resin based restorative and subsequent developments that have taken place is reviewed. The second chapter details the experimental partof this work. Polyacrylic acid, polymeric component of polycarboxylate cement was prepared by varying different experimental parameters such as temperature, initiator concentration and rate of addition of the monomer. The effect of these parameters on the molecular weight of polyacrylic acid was determined. Similarly the copolymer of acrylic acid and acrylamide was also prepared. The inorganic component of polycarboxylate cement was prepared by deactivating the commercial zinc oxide on heating at 1000 C for 30 hr. Fillers such as cryolite

7 and talc were incorporated into the zinc oxide in various proportions of 10 to 50% (w/w) in order to improve the physical properties of polycarboxylate cement. Cement samples were prepared by mixing the aqueous solution of polyacrylic acid with zinc oxide and mixtures of zinc oxide and cryolite and zinc oxide and talc on a glass slab in three powder / liquid ratios of 1:1, 1.5:1, 2:1 respectively. Also cement samples were prepared from the aqueous solution of acrylic acid and acrylamide copolymer with the above inorganic mixtures in the same manner and are designated as modified polycarboxylate cements. All the above cement samples were evaluated for working time, setting time, film thickness, solubility and disintegration, compressive strength and diametral tensile strength as per the standard specifications for polycarboxylate cement. Additional studies such as fluoride release, thermal diffusivity, wear resistance, thermogravimetric analysis and scanning electron microscopy were also carried out on these samples. Glass-ionomer cement was prepared in a similar manner by mixing the polyacrylic acid with the aluminosilicate glass prepared by fusing silica, alumina, calcium fluoride, cryolite, aluminium fluoride and aluminium phosphate. Modified glass compositions were prepared by incorporating borax in various proportions of 5 to 15% (w/w) and cements samples were prepared by mixing these glass compositions with the aqueous polyacrylic acid in P/L ratio of 1.5:1. These

8 cement samples were evaluated according to standard international specifications. The third chapter describes the results of this study. This chapter is divided into three Sections, 3.1, 3.2 and 3.3. The first Section (3.1) deals with the polycarboxylate cement and filled polycarboxylate containing cryolite and talc as fillers. It was found that incorporation of cryolite did improve the working time as well as the strength of polycarboxylate cement. A maximum increase of strength by two folds was obtained with 20% cryolite in the mix. Also cryolite incorporation made the polycarboxylate cement anticariostatic due to the release of fluoride. The samples containing 20% cryolite showed high rates of wear resistance and thermal stability. In a similar manner incorporation of talc into polycarboxylate cement also improved the working time. A maximum increase of 36% in compressive and diametral tensile strength was obtained with 10% talc in the mix. Wear resistance and thermal stability also improved at this concentration of talc in the mix. In the Section 3.2, properties of modified polycarboxylate cement based on acrylic acid and acrylamide are discussed. The samples prepared from co-polymer and zinc oxide showed improvement in the

9 properties. These properties showed further improvement in case of samples prepared with co-polymer and inorganic mixtures containing cryolite and talc. Unlike 20% cryolite in Section 3.1, it is 40% cryolite which showed maximum strength. Also inorganic mixtures containing 20% talc showed maximum strength and wear resistance. The thermal stability of the samples also improved on adding the fillers cryolite (40%) and talc (20%). In Section 3.3, the properties of glass-ionomer cement as well as modified glass-ionomer cement containing borax are discussed. Introduction of borax shortened the sdtting time of glass-ionomer cement. A reasonable setting time was obtained with glass composition containing la% borax in the mix. However, all the other properties such as strength, solubility, wear resistance and thermal diffusivity deteriorated in all proportions on borax addition.

10 CONTENTS CHAPTER 1 Page INTRODUCTION 1 Inorganic Cements Zinc phosphate cement Silicate cement Silicophosphate cement Zinc oxide - eugenol (ZOE) cements Polyalkenoate Cements Polycarboxylate cement Glass-ionomer cement Resin Cements / Restorative Resins Physico - Chemical Properties 21 of Dental Cements Working time 21 Setting time and setting chemistry 23 Compressive and diametral tensile strength 25 Solubility and disintegration 33 Fluoride release 35 Wear studies 33 Thermal diffusivity 41 Thermoanalytical characterisation 42 Scanning electron microscopic studies 44

11 Page 1.5 Purpose of Study References CHAPTER 2 2. EXPERIMENTAL Preparation of Polyacrylic Acid Effect of temperature on the molecular weight of polyacrylic acid Effect of initiator concentration on molecular weight of polyacrylic acid Effect of rate of addition of acrylic acid on the molecular weight of polyacrylic acid Molecular weight determination Preparation of Poly(Acrylic Acid-co- Acrylamide) 2.3 Preparation of Inorganic Component Deactivation of zinc oxide Preparation of mixtures of zinc oxide and 65 cryolite Preparation of mixtures of zinc oxide and 66 talc 2.4 Preparation of Glass Composition Preparation of modified glass composition Preparation of Dental Cement Compositions 67

12 2.5.1 Preparation of polycarboxylate cement Preparation of modified polycarboxylate cement Preparation of glass-ionomer and modified galss-ionomer cement Evaluation of Dental Cements Working time Setting time Compressive strength Diametral tensile strength Film thickness Solubility and disintegration Fluoride release Thermal diffusivity Wear studies Thermogravimetric analysis Scanning electron microscopic (SEM) studies References 80 CHAPTER 3 3. RESULTS AND DISCUSSION Polycarboxylate Cement Preparation of raw materials 82

13 Page Evaluation of polycarboxylate Cement Modified Polycarboxylate Cement based on Poly(Acrylic Acid-co-Acrylamide) 117' Preparation of Raw Materials Evaluation of Modified Polycarboxylate Cement Glass-ionomer Cement Preparation of raw materials Evaluation of glass-ionomer cement Conclusion & Further Scope of Work References 160