Biomedical Engineering: I Recent Developments: Proceedings of the First Southern Biomedical Engineering Conference

Biomedical Engineering I: Recent Developments covers the proceedings of the First Southern Biomedical Engineering Conference. The book presents a paper that discusses topics relevant to the development of the field of biomedical engineering. The 86 materials presented in the text are organized into 18 sessions; each session tackles a specific area of biomedical engineering. The areas covered in the book include spine biomechanics, soft tissue mechanics, biochemical engineering, bone mechanics, and medical instrumentation. The book will be of great use to researchers and professionals in the field of biomedical engineering.

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 22, 2013
• ISBN: 9781483138398

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Session 1

BIOMATERIALS

AUGMENTATION OF THE DEFICIENT ALVEOLAR RIDGE WITH HYDROXYLAPATITE

J. Kent and J. Quinn,     Dept. of Oral & Maxillofacial Surgery, Louisiana State University, 1100 Florida Avenue, New Orleans, Louisiana 70119

ABSTRACT

A polycrystalline particulate form of hydroxylapatite, was placed subperiosteally to augment deficient alveolar ridges with minor or major resorption, to enable the patients to wear dentures successfully. 55 patients had surgery, the longest follow-up was 42 months with only 10-20% resorption terminating by 6 months postoperatively. Iatrogenic complications only. Patients assessed their ability to wear dentures with stability and comfort as excellent or good using the Cornell Medical Index evaluation.

KEYWORDS

Hydroxylapatite

alloplast

alveolar ridge augmentation

bone graft substitute

preprosthetic surgery

INTRODUCTION

Approximately 25% of the population of the United States over 30 years of age are edentulous. The very high percentage of these patients have deficient alveolar ridges making it very difficult for them to wear dentures, particularly mandibular dentures. Both autogenous and homogenous bone grafts have been used to augment the deficient alveolar ridges. Problems of extensive resorption of the grafts frequently occurs resulting in a 60–100% loss. Alloplasts of ceramics, porous and solid polymers, and various metals have been also employed. Problems of migration, brittleness, soft tissue pain from denture trauma and occasional infections have resulted.

A dense polycrystalline nonresorbable form of hydroxylapatite (HA)*, free of fine pores and secondary crystalline phases with significantly greater compressive and tensile strength than previously reported sintered (HA) was used. Animal studies have shown HA to be extremely well tolerated by both the bone and soft tissues with an absence of inflammation and immune responses. HA is osteogenetically inductive and forms a strong intimate interface with bone.¹–⁴ The HA particles were used either alone in minor atrophic defects or with particulate cancellous bone for major atrophic alveolar defects.

MATERIALS AND METHODS

Preoperative Patient Considerations - Patients received 18–40 mesh HA for augmentation of minor deficiencies or HA in combination with autogenous particulate cancellous bone to correct major deficiencies. This report provides follow-up sugical and dental data on 55 patients with HA augmentation from 12-48 months.

The deficient alveolar ridges were classified and treated as follows:

Class I - adequate height and insufficient width, often with significant undercut areas (Use HA particle alone)

Class II - Ridge deficient in height and width with a knife edge. (Use HA particle alone)

Class III - Complete resorption of alveolus to basilar bone. (Use HA particles alone or with bone)

Class IV - Resorption of some basilar bone (pencil thin mandible). (Use HA particles and bone)

Patients undergoing general anesthesia were given 2 million units of aqueous penicillin intravenously at surgery. Oral phenoxy-methyl penicillin 500 mg. was given 30 minutes preoperatively to outpatients. Penicillin sensitive patients were given a suitable substitute antibiotic.

SURGICAL TECHNIQUE

All procedures using HA alone are performed under local anesthesia as an outpatient. Those requiring HA and bone are obviously performed in a hospital under general anesthesia.

The necessary number of syringes containing the HA particles are filled with patients blood at least 30 minutes before being injected into the subperiosteal pockets. Blood acts as a cohesive vehicle for HA preventing their dislodgment from the syringe during manipulation.

Augmentation of an anterior alveolar atrophy, which most often occurs in the maxilla, involved a single vertical midline incision approximately 2 centimeters in length made sharply down through the periosteum. Mucoperiosteum was then reflected on the lateral and crestal alveolus creating a subperiosteal pocket. The pocket was limited only to the area to be augmented and the opposite side is prepared in a similar fashion.

Complete mandibular or maxillary alveolar supplementation involve bilateral vertical 2 cm. incisions in the cuspid areas again down carried through the periosteum. The dissection of subperiosteal pockets was performed as previously described. Usually 3–4 syringes are necessary to augment the anterior aspect of the alveolar ridge and 6–8 syringes are needed to augment the complete ridge. The filled syringe was placed subperiosteally to the posterior ends of the pockets. In complete ridge augmentation the posterior pockets were filled bilaterally almost to the cuspid area incisions. Then the remaining anterior pocket is filled from both cuspid area incisons. Hydroxylapatite is then ejected from the syringe with the barrel of the syringe being retracted out of the incisions as the plunger maintains a constant relationship with the incision. This provides a smooth uniform placement of the material. The operator by placing his finger on the overlying mucosa molded the material to obtain the proper and contour. Mattress and interrupted sutures provided a water tight closure.

TOTAL RIDGE AUGMENTATION WITH HYDROXYLAPATITE AND BONE

Augmentation with a combination of cancellous bone and hydroxylapatite was indicated in patients with severe mandibular atrophy who required extensive alveolar ridge augmentation beyond 5 mm. The incisions and dissection when using combined material was essentially the same as previously described. Autogenous cancellous bone is harvested from the illiac crest. The bone is reduced to small particles using rongeur forceps or a bonemill and was thoroughly mixed with hydroxylapatite granules in a sterile medicine glass using a ratio of 1 gram of hydroxylapatite to 1 cc. of bone. A custom syringe or a 3 cc. syringe with the end removed is used and the mixture is packed into the syringe until it is about 3/4 full. It is then placed into the pocket and the composite materials ejected into the pocket and is manipulated and molded with fingers and instruments to the desired contour. 10–14 grams of hydroxyapatite is necessary for total ridge augmentation with bone.

POSTOPERATIVE CARE

Postoperatively antibiotic coverage is instituted for one week. Hospitalized patients were given 1 million units of penicillin intravenously every 4 hours for 24 hours and then oral penicillin VK 2 grams daily for 6 days. Appropriate antibiotics are substituted for penicillin sensitive patients. Germicidal rinses were begun as soon as possible every 4 hours while awake. Liquid and soft diet is used until dentures are constructed.

PROSTHODONTIC EVALUATION

Denture construction began as early as 4 weeks. In some cases temporary dentures were utilized and worn as soon as the augmentation site achieves stability. Various techniques were used including; definite impression procedures, schemes of occlusion and different types and designs of teeth. Patients were evaluated at 3-6 month intervals up to 24 months for denture retention stability, centric relations, esthetics and phonetics. Subjective patient parameters included; comfort, speech and abilty to chew.

RESULTS:

55 patients, 3:1 female to male, average age 56 (Fig. 1), had Hydroxyalpatite alone or with cancellous bone augmentation for deficient alveolar ridges. The mandibular alveolar ridge was augmented in 46 patients and the maxillary ridge in 9 patients. The areas involved either the entire alveolus or only the anterior or posterior areas. HA was combined with a mandibular staple in 6 patients and a visor osteotomy in 3 patients.

Figure 1

Patients were routinely observed postoperatively at 1, 6, 12, 18, and 24 months. The follow up period extended from 12–48 months with a mean follow up of 32 months. Height dimensional changes were evaluated by:

1. Cephlometric radiographs.

2. Serial panoramic radiographs.

Panoramic radiographs were evaluated by comparing preoperative, immediate postoperative and follow up films. A digital computer was used to measure the height increase and follow up changes at 10 locations both right and left sides relative to base line anatomic standard points. Dimensional width changes were evaluated by comparing preoperative and postoperative models. Caliper measurement were taken 10 mm apart, measuring from the facial to lingual aspect of the alveolus.

The results of these observations indicated less than 10% postoperative demensional reduction of the alveolar ridges with HA alone and less than 20% with HA and bone which occurred primarily due to particle consolidation for a period up to six months. No obvious changes occured after six months postoperatively.

The surgeons evaluated the status of the implant material using postoperative panoramic radiographs. The following parameters were used; implant maintenance, bone opposition, bone infiltration and overall surgical assessment. Figs. 2 & 3.

Figure 2

Figure 3

Denture satisfaction was evaluated by using the Cornell-Medical Index. This evaluates the following paramaters:

1) Denture stability, 2) Ability to chew, 3) Taste, 4) Appearance, 5) General satisfaction, 6) Denture comfort.

The results of the evaluation performed by the prosthodontist indicated that of the 55 patients wearing dentures, there were six excellent and 49 good evaluations for general denture comfort and stability. Fig. 3

CONCLUSION:

The correction of major and minor alveolar ridge deficiencies with and without undercuts has been achieved with the use of hydroxyapatite particles alone or in combination with autogenous cancellous bone with considerable success at this institution. The experiences during the past four years, using the hydroxyapatite particles, have resulted in predictably stable agumentation of the dificient alveolar ridges and satisfied denture patients.

A simple subperiostal tunneling technique and a custom plastic syringe is used to deliver the material uniformly over the alveolar ridge. Additional dental implants such as the mandibular staple or Swiss bone screws can be placed simultaneously with the hydroxyapatite augmentation or following the correction of the deficient ridge.

Denture construction can be started as early as four to six weeks postoperatively. Skin or mucosal grafting if indicated may be performed at two to three months after HA augmentation.

Consolidation producing a loss of ridge height which occurred during the first six months was found to be 10% or less with HA alone and 20% or less with HA and autogenous cancellous bone.

Denture stability is rapidly obtained and relines are much less frequent than with only bone grafting.

The use of hydroxylapatite alone or in combination with cancellous bone for augmentation of atrophic ridges has essentially eliminated the need for onlay rib and iliac crest grafting.

REFERENCES

Jarcho, M., Bolen, C.H., Thomas, M.B., Bobick, J., Kay, J.F., Doremus, R.H. Hydroxlapatite Synthesis and Characterization in Dense Polycrystalline Form,. Journal of Materials Science. 1976; 11:2027–2035.

Jarcho, M., Kay, J.F., Gumaer, K.I., Doremus, R.H., Drobeck, H.P. Tissue, Cellular and Subcellular Events at a Bone Ceramic Hydroxylapatite Interface,. Journal of Bioengineering. 1977; 1(No. 2):79–92.

Kent, J., James, R., Finger, I., Jarcho, M., Taggart, J., and Cook, S., Augmentation of Deficient Edentulous Alveolar Ridges with Win 40350 (Durapatite), A Preliminary Report, Presented at the First World Biomaterials Congress, Vienna, Austria, April 8–12, 1980.

Quinn, J. H., Alveolar Ridge Preservation with Hydroxylapatite Root Implants in Baboons - Surgical Methodology Study, Presented at Conference on New Concepts in Preprosthetic Surgery and Implant Dentistry at Louisiana State University School of Dentistry, Jan. 11–12, 1980.

---

*Durapatite, Sterling Winthrop Research Institute Rensselaer, N.Y.

MAJOR TENDON AND LIGAMENT REPAIRS WITH A DACRON PROSTHESIS (GRAFT)

Calvin H. Frazier, M.D.,     Verdugo Hills Hospital, Glendale, California

ABSTRACT

The author will present his experience, using Dacron graft material for major tendon and ligament replacements in actual clinical use. This work includes replacement of the sternoclavicular joint ligaments, acromioclavicular joint ligaments, fractures of the patella, and ruptures of the Achilles tendon. It is the author’s experience that this is an excellent replacement technique, simple to execute, and permitting early and rapid rehabilitation of the patient.

KEYWORDS

Major tendon

Dacron graft repair

MATERIALS AND METHODS

Acromioclavicular Dislocations

We first used Dacron for the acromioclavicular dislocations in 1978 and did not keep a record of all of our cases, but estimate we have 12 cases, all of which have been satisfactory both to the patient and the surgeon, using basically the technique of lashing the clavicle to the coracoid.

Postoperative care consisted of a sling for two weeks. Showering was permitted the first postoperative day. Full use of the extremity was delayed until six weeks after surgery.

Achilles Tendon Repairs

See illustrations. (Figs. 1,2,3)

Fig. 1 1st stage of Achilles tendon repair.

Fig. 2 Prosthesis passed through tendon, ready for pulling up slack and tying.

Fig. 3 Completion of Achilles tendon repair.

The first patient was a 68-year-old woman whom we first saw three months post-injury. At surgery she had a one centimeter gap at the rupture site with maximum effort at approximation of the ends of the tendon.

Four years post-operation she died, and at autopsy, the Achilles tendon appeared normal to me. The microscopic appearance of the tendon-graft interfaced showed no inflammation or foreign body reaction.

Five other Achilles tendon repairs have been done. Two of these had problems, one in an elderly diabetic patient, had a superficial infection which responded well to soaks, elevations, and antibiotics. The graft was not removed.

Another patient, 73 years old, weighing 240 pounds and being 4′10″ tall, had a dehiscence of the incision and the graft was removed. No additional repair was attempted.

Patellar Tendon Repairs

Five patients had fractured patellae repaired. (Figs. 4,5,6,7). Initially, our post-op care was the same as for the traditional patellar fracture repair. In P.E., we permitted immediate motion and weight bearing. His three week range of motion is shown here. He was a paint salesman and, I believe, an alcoholic. He returned to work three weeks post-op and has not been seen since.

Fig. 4 1st stage of patellar fracture with or without excision of fragments.

Fig. 5 Dacron prosthesis ready to be passed through proximal patella.

Fig. 6 Passing of Dacron prosthesis through patella.

Fig. 7 Completion of patellar repair.

Sternoclavicular Dislocations

One patient has had a chronic subluxation of the sternoclavicular joint repaired using a Dacron graft. (Fig. 8,9,10). She was placed on the same regime as the acromioclavicular joint patients and is now seven months post-op, and has no symptoms and an apparently normal functioning sternoclavicular joint.

Fig. 8 Holes being made in the sternum and clavicle at sternoclavicular joint.

Fig. 9 Passage of Dacron suture through the holes.

Fig. 10 Fixation of clavicle to sternum with Dacron suture.

SURGICAL TECHNIQUE

See illustrations. (Figs. 1,2,3,4,5,6,7,8,9,10).

THE FATIGUE LIFE OF INORGANIC BONE -- PMMA COMPOSITES

Y. King Liu, D. Stienstra and G. Njus,     Center for Materials Research, College of Engineering, University of Iowa, Iowa City, IA 52242

ABSTRACT

Presented in this paper are fatigue crack propagation characteristics of PMMA bone cement with addition of inorganic bone particles. It was found that crack extension rates decreased with increasing bone concentration. At the 30 percent bone level fatigue life was improved by approximately a factor of ten. In consideration of the molding characteristics of this composite, several different cement viscosities were used.

KEYWORDS

Fatigue

PMMA

Bone Cement

Inorganic Bone

INTRODUCTION

One of the major contributory factors to total joint prosthesis failure is a loosening of the cement bone interface. Failure of this interface is primarily due to two reasons: fatigue cracking in the bone cement interface and resorption of bone. Any material contains numerous microscopic loci for crack initiation, and under cyclic loading, crack extension could occur. Clinical studies indicate the cement cracking is intimately involved in premature loosening. A contributing factor to this interface failure is due to the widely different material properties of bone and bone cement.

Polymethylmethacrylate (PMMA) is routinely used as a bone cement in total joint replacements. The addition of particles to PMMA, including glass spheres (Beaumont 1977), carbon (Wright, 1982), sugar and tricalcium phosphate (Rilke, 1972), has been investigated over the years in an effort to improve the properties of the cement, i.e., to narrow the difference between the material properties of the bone and bone cement.

The ideal modifications to the material properties of the current bone cement are: 1) an increase in its fatigue life, tensile strength, and fracture toughness; 2) a decrease in its modulus of elasticity to make the cement more similar to bone; 3) the provision of biocompatibility with the human body to the satisfaction of the FDA; and finally, 4) the creation of a milieu that will allow tissue ingrowth into the PMMA. Concurrent with the above, increases in the creep characteristics or paste viscosity must be avoided. Inorganic human bone was chosen as a likely candidate to satisfy all the above requirements.

MATERIALS AND METHODS

Long bone from human cadavera was cut into manageable pieces and soaked in sodium hydroxide (0.4N) to remove the organic phase. After approximately 24 hours, the inorganic phase was ground into particles. The particles were passed through sieves to yield those in the range of 200–300 μ. The choice of particle size range was made in consideration of the work done by Predecki (1972), who determined the above hole size range to facilitate bone ingrowth. Specimens containing 0, 5, 10, 20 and 30 percent bone by weight were cast and machined.

Two sample mixing techniques were employed. The first method was addition of ground bone to a standard surgical pack of cement, i.e., constant monomer to powder ratio. In the second method, an amount of powder equal to the weight of the added bone was removed. Samples made by the second method will hereafter be referred to as powder removed (PR) samples. For each method bone was first blended with the powder before monomer addition. No attempt was made when mixing or casting to reduce porosity by artificial means such as increased temperature, pressure or ultrasound.

All material tests were conducted on a closed loop servo-hydraulic MTS test machine. Fatigue crack propagation tests were run on conpact tensile specimens according to ASTM standard E647 with sinusoidal tension-tension loading at an R ratio of 0.05. Crack lengths were monitored to .01 mm with a traveling microscope at a testing frequency of 16 cycles per second. Tensile tests were in accordance with ASTM Standard D638.

RESULTS

Data from this study are presented in the form of crack growth rate as a function of stress intensity, da/dN vs ΔK. Results from six fatigue specimens are presented in Fig. 1. A trend toward decreased crack extension rates with increasing bone concentrations may be seen. At the 30% bone level, fatigue is retarded an order of magnitude when compared to that of plain cement. There is evidenced a great deal of scatter in this plot. Each test individually contained significant scatter, and no curve smoothing routines were used for data presentation in this paper. The majority of this variability results from the nonhomogeneous distribution of micro- and macro- porosity of the specimens.

Fig. 1 da/dN vs. ΔK for PMMA with inorganic bone particles.

The trend of crack growth retardation is more vividly seen in the samples prepared by removing powder, Fig. 2. This diagram, representing five tests, shows less scatter and demonstrates more clearly the trend toward decrease in crack extension rate with an increase in bone concentration. The 20% (PR) sample shows approximately an order or magnitude improvement over the plain cement.

Fig. 2 da/dN vs. ΔK for PMMA with inorganic bone particles (PR).

In Fig. 3, the powder removed samples are compared with samples from the first group at the 10 and 20 percent concentrations. This comparison is evidence that the fatigue characteristics of the powder removed specimens are as good or better than the specimens from the first set.

Fig. 3 da/dN vs. ΔK comparison of two mixing methods.

Tensile tests were also conducted for comparison. In general, a decrease in tensile strength and a slight increase in stiffness was observed with increasing bone content.

The viscosity of the samples made by the first method increased with increasing bone content, i.e., the higher concentration samples were more difficult to stir. The viscosity of the powder removed samples, on the other hand, was comparable with or lower than the plain cement.

In all cases the crack front was within the limits for curvature prescribed by the ASTM. The fracture surfaces of the specimens containing bone are rougher and more jagged than the pure PMMA specimens when examined both by eye and with scanning electron microscope. Crack propagation also appeared more irregular for the bone-containing samples, e.g., there were more branching and directional changes.

Besides material properties, biocompatibility as approved by the FDA is an important goal. Since the bone acquired for the composite could come from the patient at the time of surgery, foreign tissue rejection should not be a problem. Hodosh, Povar and Shklar (1968) used up to 20 percent inorganic cowbone in PMMA for tooth implants in baboons without rejection.

CONCLUSION

The result of the present research is that the addition of particles of inorganic bone to PMMA significantly improves its fatigue properties. This decrease in the rate of fatigue crack propagation warrants further research to determine the optimal bone concentration and particle size for fatigue crack inhibition. In light of this study, the candidate for further study is the powder removed mixing method.

REFERENCES

Beaumont, P.W. The strength of acrylic bone cement and acrylic cement – stainless steel interfaces. J. Mat. Sci. 1977; 12:1845.

Hodosh, M, Povar, M., Shklar, G. Anatomic inorganic bone-polymethylmethacrylate endosteal dental implant. Oral Surg. 1968; 25:883.

Predecki, Paul, et al. Kinetics of bone growth into cylindrical channels in aluminum oxide and titanium. J. Biomed. Mater. Res. 1972; 6:375–400.

Rilke, A.M., et al. Porous acrylic cement. J. Biomed. Mater. Res. 1977; 11:373–397.

Wright, T.M., Burstein, A.H., Robinson, R.P. Fatigue crack propagation in polymethylmethacrylate. Trans. of Orth. Res. Soc. 1982; 7:162.

STRENGTHENING OF CALCIUM HYDROXYAPATITE BY ION EXCHANGE

C. Sombuthawee*, E.A. Monroe* and J.P. Rausch**,     *SUNY, College of Ceramics at Alfred Univ., Alfred, NY; **Dept. of Physiology, Alfred Univ., Alfred, NY

ABSTRACT

These experiments attempted to increase the flexural strength of bioceramic sintered rods of hydroxyapatite, Ca5(PO4)3 (OH). by means of ion exchange. To do this solid state reaction between the ceramic rods and powders of the reactant salts at elevated temperatures was used. The reactant salts used were Sr(NO3)2, CaCl2 and SrCl2. A strength increase occurred only when the reactant salt SrCl2 was used. A maximum increase of strength from 65 MN/m² to 79 MN/m² corresponding to a 22% increase occurred using the conditions of 650°C for 12 hours.

KEYWORDS

Bioceramic

hydroxyapatite

ion-exchange

prosthetics

chemical strengthening

INTRODUCTION

These experiments used ion exchange in an attempt to increase the flexural strength of apatite ceramic rods. The basis for accomplishing this is to develop a compressive stress in the outer surface layer of the rod by exchanging smaller ions present in the surface by larger ions from an external source. The surface compression is a result of the larger ions expanding the surface which is restrained by the underlying material, thus leading to the compressive surface stress. This technique has been applied to glass in order to achieve increased strength of up to twenty times (Doremus, 1973) and increased strengths after abrasion of greater than ten times have been reported (Nordberg,