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;...