A Positional Analyzer for Measuring Centric Slide

Centric relation (CR) has been considered mainly as a position posterior to habitual occlusion or maximum intercuspation (MI). Awareness of the tooth contacts relationship in centric relation position of the mandible and diagnosing the case from this position is essential to consistently select treatment plans that will allow to treat to or very near to centric relation occlusion. Centric slide and other occlusal relationships are conceived of as positions, which can be studied in three dimensions. Clinically, the difference between the two occlusal positions namely CR and MI (centric slide) can easily be determined, but for a more precise evaluation of its length and directions, an occlusal analysis on articulator mounted casts is necessary. Study was under taken on the mounted casts of ten subjects on a semi adjustable articulator to which a stylus and recording table was devised and attached for measurement of CR-MI slide in the three planes namely anterior-posterior, medio-lateral and superior-inferior. It was found that there was a displacement from CR to MI (centric slide) in all the three planes and numerically the mean slide was 0.688 ± 0.623, 0.261 ± 0.627 and 0.127 ± 0.541 mm in the antero-posterior, medio- lateral and superior-inferior directions respectively. The stylus and table attachment may be an accurate indirect method to measure positional changes of the condyle in 3D.     

A Technique to Stabilize Record Bases for Gothic Arch Tracings in Patients with Implant-Retained Complete Dentures

Clinicians have long expressed concern about the accuracy of the Gothic arch tracing for recording centric relation in edentulous patients. With the use of dental implants to assist in retaining complete dentures, the problem of inaccurate recordings, made for patients without natural teeth, can be significantly reduced. This article presents a technique that uses healing abutments to stabilize the record bases so that an accurate Gothic arch tracing can be made.     

长正中《牙合》型下颌全口义齿近中移位量的初步研究

目的 探讨无牙颌患者戴用长正中<牙合>型全口义齿3个月后下颌义齿的近中移位量能否满足患者长正中量的自然要求,从而检验长正中<牙合>型全口义齿的设计理论. 方法 为10例无牙颌患者制作长正中<牙合>型、线性<牙合>型和解剖<牙合>型3种全口义齿,采用哥特式弓描记装置测量无牙颌患者的长正中量,采用三维精密平移台测量3种<牙合>型下颌义齿的近中移位量.对比分析不同<牙合>型下颌义齿近中移位量的差异,并与患者长正中量进行对比. 结果 10例无牙颌患者的长正中量为(1.02±0.36)mm,3种<牙合>型下颌义齿的近中移位量分别为:长正中<牙合>型(1.016±0.348)mm,线性<牙合>型(1.092±0.448)mm,解剖<牙合>型(0.409±0.253)mm. 结论 长正中<牙合>型全口义齿能满足患者长正中量的自然要求,以及在患者正中关系位至肌力闭合道终点的位置之间无障碍的义齿设计要求.     

不同颌位记录方法对全口义齿再修复患者咀嚼效率的影响

目的比较3种记录颌位关系方法对全口义齿再修复患者不同时期咀嚼效率的影响。方法随机选择20名全口义齿再修复患者采取自身对照的方法,每位患者分别采用直接咬合法、哥特式弓描记法、哥特式弓联合面弓转移颌位关系法制作3副全口义齿,并比较不同方法下制作的义齿在患者即刻佩戴义齿时、佩戴义齿3个月后的咀嚼效率的差异。结果患者即刻佩戴义齿时咀嚼效率测定结果显示,使用哥特式弓联合面弓转移颌位关系法制作全口义齿的患者咀嚼效率明显高于使用其他2种方法制作全口义齿的患者（P〈0．05）,而使用直接咬合法与哥特式弓描记法制作全口义齿的患者咀嚼效率没有差异;佩戴义齿3个月后,3组患者的咀嚼效率无明显差异。结论使用哥特式弓联合面弓转移颌位关系法可为患者提供更可靠的颌位记录方法,可以提高患者的即刻咀嚼效率,提高患者的满意度和医生的工作效率。     

无牙颌正中关系位的哥特式弓描记与转移

目前一般认为确定无牙颌水平关系即确定正中关系位,哥特式弓描记法是唯一在确定关系时可客观观察下颌后退程度的方法。它利用固定于上下颌弓上的装置记录下颌运动时的信息,描记出雨伞状的划痕,雨伞顶点即被认为是正中关系位点。本文详细介绍了利用哥特式弓描记法记录与转移正中关系位的临床规范操作方法,主要内容包括安装描记盘、固定描记针、口内描记、记录正中关系位和转移至牙合架等操作,每一步操作都通过相应的临床图片进行详细说明。     

A Comparative Evaluation of Condylar Guidance Value from Radiograph with Interocclusal Records made During Jaw Relation and Try-in: A Pilot Study

The purpose of this study was to evaluate the reliability of programming the articulator using the radiographs and the interocclusal records made during Jaw relation (Arrow point tracing) and Try-in stage. The study comprised of 15 edentulous subjects with well formed maxillary and mandibular ridges, with no signs and symptoms of temporomandibular joint disorders and neuromuscular disorders. Digital Orthopantomograph was taken for all the subjects. The condylar guidance angles were traced on Orthopantomograph for right and left sides and the values were recorded. The protrusive interocclusal records were made at jaw relation stage and at try-in stage using bite registration paste (Bitrex- vinyl polysiloxane) for all subjects. These interocclusal records were used to programme the Semi-adjustable articulator (Hanau Wide Vue) and the condylar guidance values on the right and left sides were recorded. The condylar guidance values so obtained were compared with the values obtained by Orthopantomograph. The condylar guidance values obtained by the various procedures were subjected to statistical analysis. The results showed statistically significant difference between the condylar guidance values obtained from Orthopantomograph (Radiograph) and the condylar guidance values obtained at the stage of jaw relation and also between Orthopantomograph and condylar guidance values obtained at the stage of Try-in. Condylar guidance values obtained from the Radiographs were higher than those obtained at the stage of Jaw relation and at the stage of Try-in. However, we notice that the mean condylar guidance values obtained at the stage of Try-in were nearer to the mean condylar guidance values obtained on the Radiographs.     

Intraoral gothic arch tracing

In order to create optimum esthetics, function and phonetics in complete denture fabrication, it is necessary to record accurate maxillo-mandibular determinants of occlusion. This requires clinical skill to establish an accurate, verifiable and reproducible vertical dimension of occlusion (VDO) and centric relation (CR). Correct vertical relation depends upon a consideration of several factors, including muscle tone, inter-dental arch space and parallelism of the ridges. Any errors made while taking maxillo-mandibular jaw relation records will result in dentures that are uncomfortable and, possibly, unwearable. The application of a tracing mechanism such as the Gothic arch tracer (a central bearing device) is a demonstrable method of determining centric relation. Intraoral Gothic arch tracers provide the advantage of capturing VDO and CR in an easy-to-use technique for practitioners. Intraoral tracing (Gothic arch tracing) is a preferred method of obtaining consistent positions of the mandible in motion (retrusive, protrusive and lateral) at a comfortable VDO.     

Studies of changes in occlusion after the insertion of complete dentures. Part I*

summary The present study aims to investigate changes in the occlusion of complete dentures after their insertion. A total of 85 edentulous patients were provided with new complete dentures. Their individual hinge axes were determined using mechanical axiography and the upper finished dentures were transferred by facebows to Dentatus® articulators. The lower dentures were mounted according to an intraoral central bearing point (CBP) registration and equilibrated in terminal hinge position. An articulator specially modified for measurements in the condylar area was used. The differences between the positions of the condylar balls with CBP registration and those after equilibrating the occlusion were determined. On average, 19 days after insertion, 71 patients took part in a follow-up examination. As in the first session, the terminal hinge position was registered with the CBP method using the apex of the Gothic arch. Thus, the positions of the condylar balls immediately after the new registration could be compared with those in equilibrated in-tercuspation 3 weeks earlier. The differences were found to be 0–5 ± 0–4 mm (0.2–9 mm) in the three axes (sagittal, coronal and horizontal). They are thought to result from settling into the denture bearing tissues and also from neuromuscular adjustment of the masticatory system. Compulsory remounting of complete dentures after insertion is therefore recommended.     

Comparing condylar positions achieved through bimanual manipulation to condylar positions achieved through masticatory muscle contraction against an anterior deprogrammer: a pilot study

STATEMENT OF PROBLEM: The condylar position can vary depending on several factors. One factor is the influence of occluding teeth. If the influence from occluding teeth could be eliminated, it might be possible to evaluate the condylar position obtained from masticatory muscle contraction. PURPOSE: The purpose of this pilot study was to determine the placement of the condyles by contracted masticatory muscles without influence from occluding teeth. MATERIAL AND METHODS: For a group of 11 participants, 3 dentists were assigned, in turn, to fabricate a centric relation interocclusal record using bimanual manipulation on each member of the group. After obtaining the centric relation interocclusal records using bimanual manipulation, the records were stored in room temperature water. Subsequently, each of the 11 patients had an anterior deprogrammer fabricated and were given instructions to wear the anterior deprogrammer for 60 minutes. The anterior deprogrammer was designed with the contacting surface perpendicular to the arc of close of the mandibular incisors. In addition, the anterior deprogrammer was relined to eliminate any movement under force, and the occluding surface of the deprogrammer was free of any indentations. After wearing the deprogrammer, 4 interocclusal records (3 in a reclined position and 1 in an upright position to ensure the condylar position did not change in the upright position) were made by having the patient squeeze and close into a properly adapted, trimmed, and warmed interocclusal record. The condylar position in centric relation recorded in interocclusal records using bimanual manipulation was compared to the condylar position recorded by the contraction of the masticatory muscles against an anterior deprogrammer using a condylar position indicating device. The data were analyzed with a 2-independent-samples test of proportions, alpha=.05 (1-tail). RESULTS: The condylar positions obtained using bimanual manipulation repeated the condylar position within the 0.11-mm tolerance of the Centri-Check instrument in 33 out of 33 opportunities (100%). The condylar positions obtained by using the anterior deprogrammer technique repeated the condylar position within the 0.11-mm tolerance of the Centri-Check in 43/44 opportunities (97.7%). The sample size used in this pilot study was not large enough to detect a very small actual difference (5 percentage points or less) between the 2 methods, should such a difference exist. CONCLUSION: The results of this pilot study indicate that, without influence from occluding teeth, the contraction of the masticatory muscles places the condyles into the same position as centric relation.     

Comparison of the replicability of routinely used centric relation registration techniques

PURPOSE: This study was conducted to determine statistically the most repeatable mandibular position of 3 centric relation methods. MATERIALS AND METHODS: Three centric relation recording methods commonly reported in the literature were selected: bimanual mandibular manipulation with a jig, chin point guidance with a jig, and Gothic arch tracing. Fourteen healthy adult volunteers (7 males and 7 females), with an average age of 26.61 +/- 4.20 years and no history of extractions, temporomandibular joint dysfunction, or orthodontic treatment, were selected for the study. Accurate casts were mounted on an articulator (Denar D4A) by means of a facebow and maximum intercuspation silicone registration record. A mechanical 3-dimensional mandibular position indicator was constructed and mounted on the articulator enabling the operator to analyze the mandibular positions in 3 spatial axes (x, anteroposterior; y, superoinferior; z, mediolateral shift). Each centric relation method was recorded four times on each subject (at baseline, 1 hour, 1 day, and 1 week at approximately the same time of day). Records were transferred to the articulator, and data were extracted using a stereomicroscope modified to accept the mandibular position indicator. RESULTS: Variability within subjects ranged from 0.03 mm (left-side z axis for the bimanual method) to 1.6 mm (left-side y axis for the Gothic arch method). To indicate the least variable (most repeatable) method a comparison was made using the F test. The bimanual method was the most consistent, showing between 10.11 (p = 1) and 0.438 (p = 0.005) times less variation than the Gothic arch method (the least consistent). The repeatability of the chin point guidance method was somewhere between the other 2 methods. CONCLUSIONS: The results of this study showed that of the 3 centric relation methods evaluated, the bimanual manipulation method positioned the condyles in the temporomandibular joint with a more consistent repeatability than the other 2 methods, whereas the Gothic arch was the least consistent method.     

A clinical evaluation of materials for interocclusal registration in centric relation

Four techniques for interocclusal registrations of centric relation based on materials or combinations of materials usually utilized were tested by means of mounting of casts for a patient with partial lower edentulousness, without a free end saddle. To ensure the correct position of centric relation a Lucia jig was utilized. The following conditions for the record of posterior section were tested: registrations with wax, wax plus zinc oxide-eugenol paste, wax plus Duralay acrylic resin, and condensation silicone (putty). The evaluation was made by the measure of vertical distance between reference points in the base of the casts and calculation of variations occurring with each material. The combinations of wax plus zinc oxide-eugenol paste and wax plus Duralay acrylic resin showed the smallest variations in centric relation position.     

Evaluation of Hanau's formula in determination of lateral condylar guidance: A clinical research study

Statement of Problem:

The accuracy and reliability of the methods used for programming the semi-adjustable articulators determine the accuracy in occlusion. The current recommended average settings using the Hanau''s formula commonly used by clinicians is questionable, and thus reassessment is needed. This study was carried out to evaluate and compare the lateral condylar guidance: (1) Using the Hanau''s formula and the computerized jaw tracking device (Kinesiograph). (2) On the right and left sides using both these methods.

Materials and Methods:

A total of 20 completely edentulous patients (14 male and 6 females) within 40–60 years of age were selected. Jaw relation was recorded followed by face bow transfer. Extraoral Gothic arch tracing was recorded; three protrusive records were obtained and condylar guidance was calculated. Lateral condylar guidance was then calculated using Hanau''s formula, followed by the computerized jaw tracking device. A comparative evaluation was done of the obtained values. The same investigator worked with each of the study participants for the purpose of standardization.

Results:

The lateral condylar guidance values obtained using the Hanau''s formula ranged from 14 to 17° while those obtained using the computerized K7 jaw tracking device ranged from 8 to 40°. Bennett angle values, obtained using the jaw tracking device and Hanau''s formula showed statistically significant differences (P < 0.05) using paired t-test (at 95% confidence interval). Bennett angle values of the right and left sides found using the Hanau''s formula were almost similar. Difference in the Bennett angle values of the right and left sides were found using the jaw tracking device. However, this difference was not statistically significant (P > 0.05).

Conclusion:

Based on the results, dentist and dental technicians should consider reassessing the current recommended average settings and use of the Hanau''s formula for programming the semi-adjustable articulators.Key Words: Articulator, condylar guidance, temporomandibular joint     

Influence of the inclination of the plate of an intra-oral tracing device on the condylar position registered by tapping movement

The object of this study was to determine the best inclination of the intra-oral tracing device to get optimum condylar position with the registration of tapping movement. Three appliances with different tracing plate inclinations were used in five healthy subjects. The tracing plates were set at 0 degrees to occlusal plane (horizontal); at the angle formed by drawing a line from condylar point to the stylus position at occlusal plane (inclined); then at the angle half to inclined (half-inclined). Subjects made Gothic arch and tapping movements (n = 30) at a 30 mm interincisal distance with the head Camper plane horizontal. The incisal and condylar points were tracked with a 6-degree-of-freedom jaw movement tracking system. The location of gothic arch apex, the distribution and mean position of 30 tapping points from intercuspal position were analyzed in incisal and condylar point between the appliances. Data were analyzed with repeated measures one-way anova. Results showed that mean position of tapping points were significantly different among the appliances. Half-inclined appliance recorded tapping points in a convergent area nearer to intercuspal position (IP) than other appliances. In all appliances, the contact points of the tapping movement were anterior to Gothic arch apex.     

Temporomandibular joint function and its effect on centric relation

An occlusal analysis in relation to the TMJ radiographs will reveal factors that should be added to the purely clinical definition of centric relation. It has been previously established that bilateral asymmetric TMJ spaces and condylar retrusion or protrusion are most often associated with disc derangement and/or palpable muscle spasm.⁴ Conversely, bilateral TMJ space symmetry and condylar concentricity (condyle centered in the superior portion of the glenoid fossa) are associated with joint and muscle health. All TMJ radiographs are obtained with the teeth in the acquired centric occlusion.Centric relation is considered functional when the magnitude and direction of the centric relation deflective slide to the acquired centric occlusion correlate with the condylar displacement observed on the TMJ radiographs. For example, if the patient has a 2 mm. deflective slide straight forward, the centric relation is considered functional when the TMJ radiographs reveal equal condylar protrusion proportional to the mandibular deflection. In the judgment of the dentist, the occlusal correction of the deflective contacts will result in bilateral condylar concentricity. Conversely, centric relation is dysfunctional when the magnitude and direction of the centric relation deflective slide to the acquired centric occlusiondo not correlate with condylar position in the TMJ radiographs. When no deflective slide is present, both condyles should be concentrically located in each fossa with bilateral symmetrical joint spaces in order for centric relation to be considered functional. Dysfunctional centric, relation is often associated with disc derangement and/or palpable muscle spasm. When the centric relation is functional, the most retruded jaw position should be used. If the centric relation is dysfunctional, a therapeutic or treatment centric occlusion must be established by the dentist, utilizing the TMJ radiographs as a guide. In this situation, the most retruded position would be harmful to the patient.     

A comparative study to measure the condylar guidance by the radiographic and clinical methods

PURPOSE

The study was conducted to compare the radiographic and clinical methods of measuring the horizontal condylar guidance (HCG) values.

MATERIALS AND METHODS

The condylar guidance was measured using the radiographic (CT scan) and three clinical methods i.e. the wax protrusive records, Lucia jig record and intraoral central bearing device in 12 patients aged between 20-40 years irrespective of sex. The records were taken and transferred on the semi-adjustable articulator to record the HCG values. The CT scan was taken for 3D reconstruction of the mid facial region. Frankfort horizontal plane (FHP) and a line extending from the superior anterior most point on the glenoid fossa to the most convex point on the apex of articular eminence (AE) was marked on the CT scan. An angle between these two lines was measured on both right and left sides to obtain condylar inclination angle. Three interocclusal protrusive wax and jig records were taken and transferred to the semi adjustable articulator. Three readings were recorded on each side. Similarly the records were taken and transferred to the same articulator using the intra oral central bearing device to record the readings.

RESULTS

The statistical analysis showed insignificant differences in the HCG values between the right and left sides [(P=.589 (CT), P=.928 (wax), P=.625 (jig), P=.886 (tracer)]. The clinical methods provided low Pearsons correlation values [(R = 0.423 (wax), R = 0.354 (jig), R = 0.265 (tracer)] for the right as well as the left sides when compared with the CT values. Among the clinical methods, jig and wax method showed strong level of association which is statistically significant while the intra-oral tracer showed weak association with the other two methods.

CONCLUSION

The right and left HCG values were almost similar. The CT scan showed higher HCG values than the clinical methods and among the clinical methods, values obtained from all the methods were comparable.     

A comparison of protrusive interocclusal records to pantographic tracings

The rationale for recording protrusive mandibular movement is to accurately adjust an articulator. Techniques to record condylar inclination include radiographic interpretation, extraoral tracings, and intraoral recording materials. This study compared the protrusive settings on an articular adjusted by a pantograph to protrusive settings recorded by two intraoral recording materials, one a polyvinyl siloxane material and one a laminated, metalized wax. Pantographs were completed for 20 patients by using a kinematic hinge axis and conventional pantographic techniques. The patients also had three protrusive interocclusal records made with two intraoral registration materials completed and averaged. The average condylar inclination recorded with a pantograph (29.5 degrees) was greater than the recording by either intraoral registration material. Standard deviations ranged from 4.1 degrees to 6.6 degrees. An analysis of variance showed that the condylar inclination recorded by wax was statistically less than recorded with a pantograph. A comparison between the pantograph and the polyvinyl siloxane displayed no statistically significant difference in recording condylar inclination.     

The influence of the accuracy of the intermaxillary relations on the use of complete dentures: a clinical evaluation

The aim of this study was to investigate possible associations between the accuracy of intermaxillary relations and complete denture usage 3 months and 3 years after their insertion. A total of 600 patients were provided with new complete dentures. Willis gauge and Woelfel's method were used to assess the quality of the existing complete dentures and the use of these dentures. Three years after insertion the remaining 250 patients took part in a follow-up examination. Three months post-insertion, significant relationships were found between adequate interocclusal rest space or quality of registration of centric relation and daily wearing of complete dentures and between quality of registration of centric relation and use of dentures for eating. Three years after insertion the adaptation to denture wearing was generally satisfactory. However, no significant relationship was observed between the accuracy of intermaxillary relations and complete denture usage.     

Comparative evaluation of sagittal condylar guidance obtained from a clinical method and with cone beam computed tomography in dentate individuals

Statement of problemProgramming semiadjustable and fully adjustable articulators involves time-consuming clinical steps which can be avoided if an accurate radiographic method can accurately determine the condylar guidance angles.PurposeThe purpose of this clinical study was to compare the sagittal condylar guidance in dentate individuals as determined by a clinical method, protrusive interocclusal record, and a radiographic method, cone beam computed tomography. If the methods show a correlation, then cone beam computed tomography can be used as a time-saving method of programming an articulator for patients requiring a cone beam computed tomography scan.Material and methodsA total of 40 participants (20 men and 20 women) within the 20 to 40 years age group were enrolled according to the inclusion and exclusion criteria. Cone beam computed tomography scans were obtained, and by using an appropriate software program, the sagittal condylar guidance was measured for both sides. A protrusive interocclusal record was obtained by using polyvinyl siloxane material. The maxillary cast of each participant was mounted on a semiadjustable articulator with a facebow transfer, and the mandibular cast was mounted with a maximum intercuspal record. The protrusive record was then transferred to the articulator for programming.ResultsThe right and left sagittal condylar guidance values obtained from both the protrusive interocclusal record and cone beam computed tomography method were comparable, with no significant differences (P>.05). The difference in condylar inclination values for both sexes obtained from both methods for both sides were not statistically different (P>.05). With increasing age, condylar inclination values obtained from both methods tended to decrease. The values for sagittal condylar guidance obtained from both methods (protrusive interocclusal record and cone beam computed tomography) were comparable and correlated.ConclusionsCone beam computed tomography measurement involves stable bony landmarks and can be standardized, whereas clinical methods are time consuming and can provide inaccurate results because of the instability of the materials used to register the maxillomandibular relationship. Thus, cone beam computed tomography can be used to obtain the sagittal horizontal guidance for programming semiadjustable and fully adjustable articulators for patients requiring a cone beam computed tomography scan.     

3D-printed custom trays with a Gothic arch for centric relation recording and definitive impression making for complete dentures: A dental technique

An appliance was designed and fabricated by using computer-aided design and computer-aided manufacturing (CAD-CAM) and 3-dimensional (3D) printing to combine a custom tray with an intraoral Gothic arch. This helped simplify centric relation recording and combined definitive impression making and centric relation recording into a single step.     

Patient response to variations in denture technique. Part III: Five-year subjective evaluation.

Dentures were constructed for 64 patients by two different techniques. One technique, designated as "complex," involved more complicated procedures such as a true hinge axis location, balanced occlusion, dentures remounted on an articulator after processing with new interocclusal records, and occlusal corrections made on the articulator. The "standard" technique involved an arbitrary mounting of the maxillary cast on the articulator, arranging the occlusion with centric relation coincident with centric occlusion but without a balanced occlusion, and making occlusal corrections in the mouth. Subjective evaluations were made for each of the 64 patients at initial placement of the dentures and for all active patients at five yearly recall visits following placement. The evaluation method was designed to determine clinical differences between the dentures made by the two techniques. At the end of 5 years, the data obtained at five yearly recall visits were subjected to statistical testing. These tests were performed to determine if the technique by which the dentures were made had any effect on the performance of the dentures that could be detected clinically. The results of the test showed that there was no significant difference between dentures made using two denture techniques that could be detected by subjective means.