John K. Schulte

Comparative study of two treatment methods for internal derangement of the temporomandibular joint

Orthopedic mandibular repositioning and flat plane occlusal splint therapy were compared in the treatment of 20 patients with internal TMJ derangement with reduction. The following conclusions can be drawn. Mandibular repositioning treatment produces significant subjective and objective improvement in the dysfunction of patients with internal joint derangements with reduction. Flat plane occlusal splint treatment produces no significant change in the dysfunction level of patients with internal joint derangements with reduction. Mandibular repositioning treatment may eliminate the reciprocal click of internal joint derangement with reduction. To realize improvement in dysfunction of internal joint derangement, it appears that the reciprocal click must be eliminated. Mandibular repositioning treatment produces a significant improvement in muscle pain associated with internal joint derangement.

Dimensional stability of injection and conventional processing of denture base acrylic resin

C omplete denture fabrication is fraught with both extrinsic and intrinsic potential error. The greater part of this error can be controlled with careful clinical and laboratory technique. ’ Woelfel and Paffenbarge9 outlined the inaccuracies inherent to the use of poly(methy1 methacrylate) as a denture base material. Dimensional change during processing is one such source of error. The processing shrinkage of poly(methy1 methacrylate) resin is well documented.*” Injection processing of poly(methy1 methacrylate) denture bases was introduced by Pryor in an attempt to reduce processing shrinkage. More recently a continuous-pressure injection technique has been developed (SR-Ivocap, Ivoclar AG, Schaan, Liechtenstein). As discussed by Schmidt9 the process claims to deliver reduced processing error and increased resin density through layered curing of the resin and no processing flash. Trituration of the liquidpowder system is mechanically performed in prepackaged capsules in an attempt to produce a more even mix resulting in a homogeneous denture base. The mixed resin is injected into the flask under continuous pressure during the processing.” This study determined the dimensional changes of heat-cured poly(methy1 methacrylate) resin processed by the injection processing system compared with that processed by a conventional compression packing technique.

Crown-to-implant ratios of single tooth implant-supported restorations

STATEMENT OF PROBLEM The crown-root ratio guidelines used to establish a prognosis for teeth serving as abutments are commonly applied to a dental implant-supported restoration or potential implant site. These guidelines are generally empirical and therefore lack scientific validation. PURPOSE The purpose of this study was to first determine the crown-implant ratios of single tooth implant-supported restorations, and then to compare the crown-implant ratios to the guidelines established for the crown-root ratios of natural teeth. MATERIAL AND METHODS A retrospective cohort study design was used. The cohort was composed of subjects (n=294) having 1 or more single tooth implants (Bicon) placed between May 1992 and April 2004. A chart review was conducted to obtain radiographs in which the entire crown and implant were visible. The length of the crown and implant were measured directly from the radiographs using magnification to calculate the crown-to-implant ratio. The length of the crown was divided by the length of the implant to determine the crown-implant ratio. Calculations were made to within 0.1 mm. Implant failure was recorded and defined as removal of the implant for any reason. Data were analyzed with descriptive statistics. RESULTS A total of 889 single tooth implants from 294 patients were measured and included in the study. The mean (SD) follow-up time was 2.3 (1.7) years, with a range of 0.1 to 7.4 years. Sixteen failures were recorded for a survival rate of 98.2%. The crown-implant ratios ranged from 0.5:1 to 3:1. The mean (SD) crown-implant ratio of implants in function was 1.3:1 (0.34). The mean crown-to-implant ratio of failed implants was 1.4:1 (2.5). CONCLUSIONS The results of this study suggest that the crown-to-root ratio guidelines associated with natural teeth should not be applied to a potential implant site or existing implant restoration. The crown-to-implant ratios of those implants that were in function were similar to those implants that failed.

Forces and moments generated at the dental incisors during forceful biting in humans

A miniature load sensor capable of measuring all forces and all moments simultaneously at a single location in space was used to assess the magnitude and direction of loads that affect the dental incisors during forceful, static biting. While prior approaches have not measured all necessary six degrees of freedom during biting, the complete set of loads is needed to serve as realistic boundary conditions for analytical or computational models of mandibular mechanics. Four subjects were asked to perform controlled and repetitive edge-to-edge incisal biting activities. Customized devices were used to rigidly hold the load sensor in place at pre-specified tooth separations of less than 1 mm. The results yielded force resultants with a magnitude range of 24.5 to 28.4 N. This range was intentionally limited in magnitude to avoid damage to the internal strain gauge assembly of the sensor. In all cases, the highest force component was oriented upwards. An additional simultaneous moment resultant (range: 8.9-17.0 N cm) with a main moment component oriented backwards and downwards towards the oral cavity was also detected. These data suggest that in order for the biting loads to be composed of six DOF, the remaining forces acting on the mandibular force system (i.e. muscular and/or articular) may indeed be non-coplanar and non-concurrent. Although useful for static biting activities, the bulk of the sensor would probably preclude meaningful measurements during dynamic events such as chewing or swallowing.

Crown-to-Implant Ratios of Short-Length Implants

Excessive crown-implant ratios have been cited in the literature as being detrimental to long-term implant survival. However, unfavorable crown-implant ratios have not yet been established. The primary aim of this study was to determine the crown-implant ratios of single-tooth implant-supported restorations on short-length implants in a clinical practice, and to evaluate the health of these implants via mesial and distal first bone-to-implant contact levels. Additionally, the relationship between crown-implant ratios and proximal first bone-to-implant contact levels will be evaluated. In this retrospective cohort study, the cohort was composed of 194 patients who possessed at least 1 single 5.7 mm or 6 mm length plateau design implant-supported restoration that had been surgically placed between February 1997 and December 2005. A chart review was performed to acquire the most recent radiographs in which both the entire crown and the implant were visible. The length of the crown and implant was measured directly from the radiographs using consistent magnification to calculate the crown-implant ratio. Mesial and distal first bone-to-implant contact levels were measured using 3 times magnification and were mathematically corrected for distortion. The last available radiograph was used to measure bone levels. Follow-up time was calculated from the day of implant placement to the date of the last available radiograph. Statistical analyses with analysis of variance mixed models were used. Data from 309 single implant-supported fixed restorations were tabulated and included in the study. The mean (SD) follow-up time was 20.9 (23.2) months, with a range of 15.6 to 122.8 months. The mean crown length (SD) was 13.4 (2.6) mm, with a range of 6.2 to 21.7 mm. The mean (SD) crown-implant ratio was 2.0 (0.4) and ranged from 0.9 to 3.2. The average mesial and distal first bone-to-implant contact levels (SD) measured from the radiographs were -0.2 (0.7) mm and -0.2 (0.9) mm, respectively. No statistically significant relationship was observed between increasing crown-implant ratios and decreasing mesial and distal first bone-to-implant contact levels around the implant with P values of .94 and .57, respectively. In this investigation, mesial and distal first bone-to-implant contact levels on short-length implants fall within the established guidelines for success. Also, there are no associations between crown-implant ratios and first bone-to-implant contact levels.

Fractures related to occlusal overload with single posterior implants: a clinical report.

This clinical report describes 2 patient situations in which fractures related to occlusal overload occurred with a single posterior implants. The initial clinical presentation of both patients appeared to be screw loosening, but upon further examination, implant and abutment fractures were identified. Several factors are described that have been implicated in the etiology of implant fractures, including occlusal overload, implant location, inadequate fit of the prosthesis, design of the prosthesis, progressive bone loss, metal fatigue, implant diameter, manufacturing defects, and galvanic activity. This article describes the management of implant and abutment fractures and discusses possible mechanisms of failure for the patient situations presented. Careful treatment planning and execution of implant therapy is necessary to minimize the risk of implant and component fractures.

Reliability of the evaluation of occlusal contacts in the intercuspal position

Reliability of clinical measurement is essential to any clinical discipline. This investigation assessed intraexaminer and interexaminer reliability achieved in identifying contacting teeth in the intercuspal position. Shim stock and an articulating film were compared in the evaluation of occlusal contacts of 337 antagonist occlusal pairs in 24 young adults by two examiners. Results were compared by use of a simple proportion of agreement and, when possible, the Kappa statistical test that corrects for chance agreement. Shim stock displayed better reliability than articulating film and appeared suitable for clinical measurement of occlusal contacts in intercuspal position.

Three-dimensional analysis of cusp travel during a nonworking mandibular movement

patient is asked to bite together. The high spots are marked, as are the areas that bind the gauge from pulling through freely. The tooth is then reduced appropriately on the marked areas. If the gauge doesn’t pull through, the process is repeated: marking with articulating paper, grinding, and checking for clearance. The process is repeated as often as necessary until the gauge pulls through, which indicates the desired reduction. If it is inconvenient to customize and store blotting paper, a rubber band may be substituted. The common variety used by the U.S. Postal Service to bind a packet of letters is suitable. The rubber band measures about %6 inch thick (1.1 mm), % inch wide, and 3 inches long. The rubber band may be cut to a length of twice the width of the occlusal marking paper. One advantage is that the rubber band can be sterilized and used repeatedly. The flexibility of a rubber band to ride over cusps is undeniable.

The hinge axis transfer procedure: A three-dimensional error analysis

T he face-bow transfer procedure has been controversial for many years. Stansbery’ described its use as futile and of no practical value, while Logan2 and others described its advantages and advocated its use. Several authors believe that it is necessary to accurately locate the true transverse hinge axis,3-6 while others argue that an arbitrary axis will produce acceptable clinical results.’ Use of the face-bow is generally acceptable and is incorporated into the curriculum of most dental schools. If a face-bow is not used, or if an arbitrary face-bow is used, an occlusal error is introduced. This results when the vertical dimension of the articulator is changed from that of the centric relation record to initial tooth contact and occurs because of the difference in rotational centers of the patient’s mandible and that of the articulator. The principal advantage of the face-bow is that centric relation records of various thicknesses can be used when the mandibular cast is mounted to an axis opening instrument without occlusal error. Theoretically, the occlusal error is zero if the true hinge axis is located on the patient and transferred to the instrument. Research has not considered the three-dimensional occlusal error that occurs as a result of error in bilateral location of the true hinge axis points on the patient. The purpose of this article is to quantify occlusal errors three dimensionally at the first molar region when an error is made in bilateral location of the true hinge axis.

Wear resistance of isosit and polymethyl methacrylate occlusal splint material

Abstract Simulated occlusal wear utilizing the artifical mouth included natural enamel against isosit and polymethyl methacrylate splint materials. The results reported in volume loss (mm 3 ) demonstrated the isosit material to be 55–67% more resistant to wear than polymethyl methacrylate. No wear occurred on the enamel surface opposing either splint material.