John D. Rugh

Determinants of masticatory performance in dentate adults

Masticatory performance results from a complex interplay of direct and indirect effects, yet most studies employ univariate models. This study tested a multivariate model of masticatory performance for dentate subjects. Explanatory variables included number of functional tooth units, bite force, sex, age, masseter cross-sectional area, presence of temporomandibular disorders, and presence of diabetes mellitus. The population-based sample consisted of 631 dentate subjects aged 37-80 years. Covariance structure analysis showed that 68% of the variability in masticatory performance could be explained by the combined effects of the explanatory variables. Age and sex did not show a strong effect on masticatory performance, either directly or indirectly through masseter cross-sectional area, temporomandibular disorders, and bite force. Number of functional tooth units and bite force were confirmed as the key determinants of masticatory performance, which suggests that their maintenance may be of major importance for promoting healthful functional status.

Health-related quality of life and psychosocial function 5 years after orthognathic surgery

This prospective, multisite, randomized clinical trial evaluated the long-term health-related quality of life and psychosocial function of 93 patients after bilateral sagittal split osteotomy to correct Class II malocclusion. Patients were evaluated approximately 2 weeks before surgery, and 2 and 5 years after surgery. Scores from the Sickness Impact Profile psychosocial dimension and all of its components showed significant improvement from presurgery to 2 and 5 years postsurgery (P <.05). The overall dimension score also showed significant improvement (P <.05). Change between 2 and 5 years postsurgery was not significant, demonstrating that the improvement was stable between 2 and 5 years. The Oral Health Status Questionnaire showed significant improvement at 2 and 5 years relative to presurgery (P <.05). These improvements also remained stable between 2 and 5 years, with the exception of general oral health. The Symptom Checklist 90 Revised demonstrated significant improvements from presurgery to 2 and 5 years after surgery (P <.05) in all areas except somatization. Results other than somatization did not change significantly between 2 and 5 years, showing that improvements were stable. The 7-point satisfaction scale showed that patients were satisfied with postsurgical results, and their satisfaction was maintained 5 years after surgery. It is concluded that general health-related quality of life, oral health-related quality of life, and psychosocial function show significant improvements after bilateral sagittal split osteotomy, and the improvements are stable between 2 and 5 years after surgery.

Association of Salivary Flow Rates with Maximal Bite Force

Mean salivary secretion and bite force decrease with advancing age. Previous studies have shown that salivary flow rates are influenced by mastication. In the present study, we examined the relationship between salivary flow rates and maximal bite force in a community-based sample of men and women 35 years of age or older. Salivary flow rates for unstimulated whole and unstimulated submandibular/sublingual (SMSL) saliva as well as citrate-stimulated parotid and SMSL saliva were measured in 399 subjects. Bite force was assessed with a bilateral force transducer. Pearson correlation analysis yielded significant positive correlations between bite force and flow rates for unstimulated whole saliva (r = 0.24, p < 0.0001), stimulated parotid saliva (r = 0.13, p < 0.03), unstimulated SMSL (r = 0.14, p < 0.0001), and stimulated SMSL (r = 0.16, p < 0.003). When adjusted for age and gender, the partial correlations between bite force and salivary flow rates remained significant for unstimulated whole saliva (r = 0.10, p < 0.05), stimulated parotid saliva (r = 0.13, p < 0.02), and stimulated SMSL saliva (r = 0.14, p < 0.006). Subjects were divided into four groups based on their maximal bite force score (low, medium low, medium high, and high). For each saliva type, the flow rate of the high-bite-force group was significantly greater than that of the low-bite-force group as well as that of the medium-high-bite-force group. These results confirm an age-related decrease in bite force and salivary flow rates and show that, regardless of age or gender, bite force is correlated with salivary flow.

The use of bio-feedback devices in the treatment of bruxism.

The results of pilot investigations recently completed at the UCLA TMJ Clinic suggest that the treatment and investigation of self-destructive oral habits may be facilitated by the use of portable muscle hyperactivity devices worn by patients (Figure I). The need for these devices is supported by considerable evidence suggesting that abnormal oral habits such as bruxism may cause or contribute to excessive tooth wear, trauma from occlusion, and TMJ pain and dysfunction. Treatment and investigation of these problems has been difficult because the habits involved arc usually performed unconsciously; thus patients are unable to report the occurrence, nature, or frequency of their habit. The present investigators have developed a portable muscle biofeedback unit that delivers an audible “warning” tone should the patient clench or grind his teeth (Figure 2).

Oral Function and Diet Quality in a Community-based Sample

Overall diet quality indices, such as the Healthy Eating Index (HEI), are preferred for epidemiological studies, yet studies in dentistry have focused on isolated dietary components. This study investigated the influence of socio-demographic and masticatory variables (masticatory performance, bite force, number of posterior functional tooth units, TMJ disorder, and dentition status) on overall diet quality in a community-based sample (n = 731). Cross-sectional data were derived from clinical examinations, bite force recordings, masticatory performance measurements, and two 24-hour dietary recalls. Females, European-Americans, and older subjects had better HEI scores than males, Mexican-Americans, and younger subjects, respectively. Income, education, and the masticatory variables were not related to diet quality. Analyses according to dentition status (good dentition, compromised dentition, partial denture, and complete dentures) showed no inter-group differences for HEI except for the age groups. The results suggest that the chewing-related factors evaluated in this sample are not predictors of overall diet quality across the socio-demographic groups.

Short-term changes of condylar position after sagittal split osteotomy for mandibular advancement.

OBJECTIVE The goal of this study was to quantify condylar position changes after mandibular advancement surgery with rigid fixation (screws). Radiographic changes in condylar position were determined in all planes (X, Y, and Z). Computed tomography with image reconstruction was used. STUDY DESIGN A consecutive population of patients who elected to have rigid fixation for surgical stabilization method were studied (n = 21). Computed tomography data were acquired in the axial plane through use of abutting 1.5-mm-thick slices. Data acquisition occurred 1 week preoperatively and 8 weeks postoperatively. Measurements were made from 2-dimensional reconstructions. RESULTS The averages were as follows: lateral displacement from midline, 1.2 mm (55% of patients); medial displacement from midline, 1.5 mm (45% of patients; range, 3.2 mm); condyle angle increase from coronal plane, 3.5 degrees (60% of patients); condyle angle decrease from coronal, 4.3 degrees (40% of patients; range, 8.5 degrees); superior rotation of proximal segment, 3.2 degrees (39% of patients); inferior rotation of proximal segment, 8.6 degrees (61% of patients; range, 15.6 degrees); superior displacement, 1.2 mm (60% of patients); inferior displacement, 1.0 mm (40% of patients; range, 2.5 mm); anterior displacement, 1.6 mm (33% of patients); posterior displacement, 1.6 mm (67% of patients; range, 2.8 mm). CONCLUSIONS Changes occurred in all planes, but the most common postoperative condyle position was more lateral; with increased angle, the coronoid process was higher and the condyle was more superior and posterior in the fossa.

Technical factors accounting for stability of a bilateral sagittal split osteotomy advancementWire osteosynthesis versus rigid fixation

OBJECTIVE Relapse after bilateral sagittal split osteotomy has been attributed to various technical factors that are inherent in the surgical procedure. The purpose of this article was to analyze technical factors that predispose to relapse when wire or rigid fixation is used. STUDY DESIGN Patients were randomized to either rigid or wire osteosynthesis. Cephalometric radiographs were obtained and digitized at multiple time periods before and after surgery. Data were analyzed through use of 2-sample t tests and stepwise regression analyses. RESULTS Multivariate analysis indicated that the following factors correlated with relapse: initial advancement, change in ramus in inclination, change in the mandibular plane, and fixation type. CONCLUSIONS Relapse increased with the amount of initial advancement and, to a lesser extent, with control of the proximal segment and change in the mandibular plane. These factors are similar for wire osteosynthesis and rigid fixation.

Five-year outcome and predictability of soft tissue profiles when wire or rigid fixation is used in mandibular advancement surgery

The purpose of this study was to follow the covariation of hard and soft tissue changes in Class II malocclusion subjects who received a bilateral sagittal split osteotomy. The subjects were randomized to receive wire or rigid fixation after the surgery. Subjects in the rigid group (n = 78) received 2-mm bicortical position screws, and those in the wire group (n = 49) received inferior border wires and 6 weeks of skeletal intermaxillary fixation with 24-gauge wires. Additionally, some subjects received genioplasty in both the rigid (n = 35) and the wire groups (n = 24). Soft and hard tissue profile changes were obtained from cephalometric films immediately before surgery and at various times up to 5 years postsurgery. Soft and hard tissue profile changes were referenced to a cranial-base X-Y coordinate system. Horizontal changes in mandibular incisor, lower lip, B-point, soft tissue B-point, pogonion, and soft tissue pogonion were calculated at each time. There was considerable skeletal relapse in the wire fixation group. Bivariate correlations and ratios between the hard and soft tissue changes were calculated for each time period. Hard to soft tissue correlations were the highest at the earlier times, although the ratios varied among the 4 groups. These results provide a solid basis for both short-term and long-term prediction.

A comparative study of skeletal and dental stability between rigid and wire fixation for mandibular advancement.

This study examined the skeletal and dental stability after mandibular advancement surgery with rigid or wire fixation for up to 2 years after the surgery. Subjects for this multisite, prospective, randomized, clinical trial were assigned to receive rigid (n = 64) or wire (n = 63) fixation. The rigid cases received three 2-mm bicortical position screws bilaterally and elastics; the wire fixation subjects received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Skeletal and dental changes were analyzed using the Johnstons analysis. Before surgery both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior advancement of the mandibular symphasis was 5.5 mm (SD, 3.2) in the rigid group and 5.6 mm (SD, 3.0) in the wire group. Two years after surgery, mandibular symphasis was unchanged in the rigid group, whereas the wire group had 26% of sagittal relapse. Dental compensation occurred to maintain the corrected occlusion, with the mandibular incisor moving forward in the wire group and posteriorly in the rigid group. However, at 2 years after surgery, when most subjects were without braces, the overjet and molar discrepancy had relapsed similarly in both groups.

Effects of surgical mandibular advancement and rotation on signs and symptoms of temporomandibular disorder: A 2-year follow-up study

INTRODUCTION The possible effects of orthognathic surgery on signs and symptoms of temporomandibular disorder (TMD) are still controversial. We prospectively investigated the association between the amount of advancement and rotation of the mandible during bilateral sagittal split osteotomy (BSSO) and the development of TMD signs and symptoms. METHODS Class II patients (n = 127) received mandibular advancement with BSSO. We used factorial analysis of covariance to assess whether the magnitude (< or > or = 7 mm) and the direction (clockwise or counterclockwise) of the movement were associated with the onset or worsening of TMD signs and symptoms during 2 years of follow-up. RESULTS Counterclockwise rotation of the mandible was associated with more muscle tenderness, especially in patients receiving long advancements. The combination of long advancement with counterclockwise rotation was also associated with increased joint symptoms. All symptoms declined over the 2-year follow-up period. CONCLUSIONS Counterclockwise rotation of the mandible is related to a slight increase in muscle symptoms after BSSO. The combination of counterclockwise rotation with long advancement also might increase joint signs and symptoms. All symptomatology tended to decline over time, suggesting that the amount of advancement and mandibular rotation should not be considered as risk factors for the development of TMD in patients without preexisting conditions.