Modeling of jaw biomechanics in the reconstructed mandibulectomy patient.

STATEMENT OF PROBLEM: Biomechanics of occlusal force and indirect calculation of temporomandibular joint loading in patients after surgery for head and neck cancer is poorly understood. PURPOSE: This study compared occlusal force values of 6 mandibulectomy subjects with reconstructed mandibles to 6 noncancer subjects with intact mandibles and reports occlusal force predictions from a developed computer model simulation of both a mandibulectomy subject with a reconstructed mandible and noncancer subject with an intact mandible. MATERIAL AND METHODS: Maximum occlusal force was recorded at the first molar and incisal edge in 6 mandibulectomy subjects who had bony reconstruction of the mandible and 6 noncancer subjects with an intact mandible. Clinical data were then qualitatively compared with occlusal force values generated from an existing computer model simulating an average adult, and a developed model simulating an average mandibulectomy subject who had bony reconstruction of the mandible. The biomechanical parameters modeled also included an estimation of joint force magnitude and direction when biting with maximal force on the first molar. RESULTS: Clinical data revealed no significant differences in occlusal force between the 6 mandibulectomy subjects with bony reconstruction of the mandible and 6 noncancer subjects with an intact mandible; however, average molar and incisal occlusal force values were 22% and 32% less in mandibulectomy subjects with bony reconstruction. Computer simulations of a reconstructed mandibulectomy subject predicted that reconstructed subjects would have 45% less molar occlusal force, 50% less incisal occlusal force, and a higher joint/tooth force ratio compared with a simulated noncancer patient with an intact mandible. CONCLUSIONS: There were no significant differences in first molar or incisal occlusal force between reconstructed mandibulectomy subjects and noncancer subjects with intact mandibles. Trends calculated from computer simulations were consistent with clinical findings.

A comparison of masticatory function in patients with or without reconstruction of the mandible.

BACKGROUND: The functional benefits of mandibular reconstruction following a composite resection remain unclear. Although microvascular surgical techniques have dramatically increased the predictability of bone and soft-tissue reconstruction towards presurgical anatomic norms, the specific factors responsible for improved function remain controversial. Objective measures of masticatory function need to be more clearly determined before the predictability and efficacy of reconstructive approaches is established. METHODS: We evaluated objective measures of oral function and patient reports of function in 10 reconstructed mandibulectomy patients, 10 without reconstruction, and 10 controls. Measures of oral function included bite force assessed at the first molar and incisal edge, a measure of tongue and cheek function, and patient reports of food they could eat. RESULTS: Both reconstructed and nonreconstructed patients presented decreased biting force, a more restricted diet, and compromised cheek and tongue function as compared with normals. However, reconstructed patients had significantly better measures of tongue function and ability to eat a varied diet than did nonreconstructed patients. Of the objective measures used to measure masticatory performance, bite force was poorly correlated, whereas measures of tongue function strongly correlated with successful mastication. CONCLUSION: Both reconstructed and nonreconstructed patients presented with a significant functional deficit when compared with normals, with reconstructed patients having better overall function than nonreconstructed patients.

Incidence of various classes of removable partial dentures.

The purpose of a classification for removable partial dentures (RPDs) is to simplify identification and enhance its teaching. A classification also allows a longitudinal comparison of various classes of RPDs to determine whether the teaching of RPD design is consistent with the relative frequencies of RPD use. This study surveyed the types of removable partial dentures being fabricated in a regional dental laboratory and compared these findings with data from previous studies. Results indicate that mandibular RPDs are more common than maxillary RPDs and the class I mandibular RPD is the most common type of RPD for either dental arch. A palatal strap was the most frequently used maxillary major connector and a lingual bar was used three times more often than a lingual plate in the mandibular arch. Cast circumferential clasps were used twice as often as RPI clasp designs. The percentage of Kennedy class I RPDs was 40%, class II 33%, class III 18%, and class IV 9%. Comparisons with a previous study indicate the percentage of Kennedy class II has increased, whereas class I, class III and class IV RPDs have not changed significantly. Findings of the study indicate that the frequency of use of the various types of RPDs have changed in the past 30 years.

Osseointegration of two types of implants in nonhuman primates.

Branemark developed a dental implant that can reliably replace missing teeth. The success of this implant is attributed to a direct connection of bone with the implant (osseointegration). Several implants, including the Core-Vent implant, adhere to the requirements described by Branemark and his coworkers to achieve osseointegration, yet no studies have attempted to directly compare osseointegration of the Biotes implant with other implants. This study directly compared the response of bone to the unloaded and occlusally loaded Core-Vent and Biotes implants at the light microscopic level by using the nonhuman primate model. Histologic examination revealed that both Core-Vent and Biotes implants achieved osseointegration and maintained the direct contact with bone after 5 months of occlusal loading.

Occlusal considerations for partially or completely edentulous skeletal Class II patients. Part II: Treatment concepts.

Four basic concepts must be considered when developing the prosthetic occlusion for skeletal class II patients: (1) Centric relation must be used as a reference position to relate the mandible to the maxillae; (2) the posterior denture teeth must be positioned close to their former positions; (3) freedom of movement must be created in eccentric movements; and (4) multiple occlusal contacts must be provided in centric and eccentric positions. We have described a method that incorporates these basic concepts and provides a harmonious occlusal arrangement for both edentulous and partially edentulous class II patients.

Occlusal considerations for partially or completely edentulous skeletal class II patients. Part I: Background information.

Although approximately 15% of the population may be classified as having the skeletal class II relationship, this group of patients is far from homogeneous. Two prototypes were used to delineate various problems in the prosthodontic occlusion that dentists may encounter with these patients. A satisfactory occlusion is difficult to achieve because of skeletal discrepancies, limited space for occlusal contact, steep guidance factors, and the necessity for multiple eccentric occlusal contacts because of the significant range of mandibular motion.

Autogenous bone grafts for atrophic edentulous mandibles: a final report.

While autogenous bone augmentations for atrophic edentulous mandibles are not the ideal solution for this problem, we do not share the pessimism of other investigators. The average loss of bone over the 92-month observation period was 60% for this small sample of eight patients. However, there was an 81% gain in bone height in the premolar-molar regions when compared with presurgical measurements. Seven of the eight patients believed these procedures were beneficial.

A review of techniques of crown fabrication for existing removable partial dentures.

Fourteen methods for making a crown to fit an RPD have been described. The techniques have been briefly reviewed and classified to indicate whether crown pattern construction is direct, direct-indirect, or indirect, and whether the RPD is needed in the laboratory phase. The choice of a technique appears to be a matter of personal preference for the dentist.

Mandibular augmentation with hydroxyapatite.

This study investigated the success of hydroxyapatite mandibular augmentation in nine patients, the histologic response around hydroxyapatite, and the effect of collagen in localizing hydroxyapatite. It can be concluded that hydroxyapatite is biocompatible, causes minimal inflammatory response, and can increase denture retention. However, a large number of patients develop lip paresthesia, and hydroxyapatite migrates. Paresthesia might be avoided by altering the surgical technique to avoid manipulation of the mental nerve, and collagen might be a useful binder to confine hydroxyapatite particles. Further studies are in progress to develop new methods to place the hydroxyapatite and materials to confine it.

Evaluation of patients for preprosthetic surgery.

The success of preprosthetic surgery and subsequent complete dentures depends not ony on the technical success of the procedures but also on the patient's satisfaction with the outcome. Studies of patients' satisfaction with their complete dentures confirm the experience of prosthodontists--that the problems described by patients do not always correlate with detectable anatomic deficiencies or technical faults in the prostheses. Since the responsibility for patient care is shared by both the surgeon and the prosthodontist, it is important that both specialists by involved in the screening process and evaluation of patients for preprosthetic surgery, prior to treatment. This article describes the basic criteria for patient evaluation, including signs that might indicate a poor prognosis for preprosthetic surgery. Everyone benefits if a realistic prognosis for the proposed combined treatment can be established before therapy is begun.

Canalicular communication in the cortices of human long bones.

A scanning electron microscopic (SEM) cast method that has been utilized to examine the internal structure of dentine was modified to examine canalicular communications in the cortices of a human femur and ulna. Although some preparations in which all of the matrix was removed were examined, etched preparations were found to be the most informative. Casts of lacunae and canaliculi along with the underlying matrix could be visualized in these preparations. In the femur, whose cortex exhibited a typical lamellar pattern, canalicular communication was seen between first and second generation osteons and occasionally between osteons and interstitial regions. The interstitial regions in the ulna appeared to be primarily woven rather than lamellar bone. Extensive communication between the outermost lacunae of osteons and interstitial regions was observed in the ulna.

Maxillofacial prosthetics in the dental school curriculum.

A survey was sent to all dental schools in the United States to ascertain what type of training in maxillofacial prosthetics was included as a separate course or included within other courses. Eighty-six percent of the questionnaires were returned. The results indicated that, while only 31% of the respondents offered a specific course in maxillofacial prosthetics, much of this information was offered in several other dental school courses. Specific information should be included in the curriculum on subjects such as radiation therapy and chemotherapy. However, the emphasis should be aimed at familiarizing the dental student with the objective and scope of maxillofacial rehabilitation without providing details regarding the fabrication of the infinite variety of maxillofacial prostheses. This general information is essential so that dental students realize that appropriate treatment of carcinoma patients includes prosthetic rehabilitation and they can counsel and refer their patients appropriately.

Current concepts in cranioplasty.

A review of the methods of cranioplasty has been presented. A method of prefabrication of an alloplastic cranial implant has been described as well as a review of 40 patients with whom this technique was used.

Autogenous bone graft procedures for atrophic edentulous mandibles.

Using a joint oral surgery-prosthodontic team approach, five patients with extreme atrophy of the edentulous mandible were selected for augmentation of the mandible with autogenous bone grafts from the crest of the ilium. All were wearing restorations considered adequate, but they had difficulty tolerating the lower dentures. An extraoral submandibular surgical approach was employed with few postoperative complications. Sulcus extension procedures were unnecessary after surgery, and four of the five patients received lower prostheses in approximately 3 months. The oral surgeon, the prosthodontist, and the five patients considered the results successful.

Radiation complications in edentulous patients.

Complete dentures were fabricated for 88 patients following completion of cancericidal doses of radiation therapy to the head and neck regions. All were followed for at least 6 months after delivery. All patients received dentures resting within the radiation field. Three patients developed osteoradionecroses directly attributable to their dentures. These three had been dentulous prior to therapy and had either pre- or posttreatment extractions. Of the 58 patients who had been edentulous prior to therapy, none developed osteoradionecrosis. Five patients developed soft tissue necroses secondary to the use of dentures.