Computer-aided evaluation of occlusal load in complete dentures

History of materials used for recording static and dynamic occlusal contact marks: a literature review

In the discipline of prosthetic dentistry it is important not only to examine the occlusion, but to be able to record, store, and transfer the information. Over the years many occlusion testing materials have been used. It has been suggested the clinical recording and transfer of information using waxes and other occlusion recording materials have disadvantages relating to inaccuracy and problems of manipulation. Therefore, there has been introduction of many new systems for recording occlusion contacts to overcome such problems. The correct physiological recovery of occlusion posses as much a challenge as ever for every dentist and technician. Even the smallest high spots measuring just a few microns can cause dysfunctions like temporo-mandibular pain. Occlusal proportions are being constantly changed with every procedure. Therefore, an understanding of the synergy of the teeth in static and dynamic occlusion forms the basis of good dentistry. The purpose of this review article is to give and overview of the various materials and methods that have been used to record occlusal contact marks. Key words:Occlusal contact marks, Occlusion indicators, Occlusion test materials, Occlusion recording materials.

Influence of the fast-processing technique on the number of the occlusal contacts and occlusal vertical dimension of complete dentures

AIM

Occlusal errors during acryl processing affect the retention and stability of complete dentures. The aim of the present study was to assess the influence of a short curing technique on the number of occlusal contacts and the occlusal vertical dimension (OVD) of complete dentures.

MATERIALS AND METHODS

Complete dentures were prepared. The number of occlusal contacts was recorded in centric relation (CR) using 60 µ articulation paper. The OVD was recorded with the waxed trial denture in place. Dentures were then invested and processed with compression molding and short cure water bath technique. The number of occlusal contacts was recorded again. The amount of pin opening was measured for all of the complete dentures on the articulator. Data were analyzed with paired t-test to determine the alterations.

RESULTS

The mean number of occlusal contacts before and after processing was 10.9 ± 2.4 and 6.3 ± 3.1 respectively (4.7 ± 1.9 decrease; p < 0.001). A 2 mm mean increase in OVD was observed in 47.7% of the dentures with < 6 occlusal contact changes and 88.9% of the dentures with ≥ 6 occlusal contact changes (p < 0.003). A significant change in the number of occlusal contacts was associated with an OVD increased up to two times.

CONCLUSION

The short curing technique seems to be related to the decreased occlusal contacts and increased OVD. CLINICAL SIGNIFICANCES: More time is needed to adjust the occlusal errors of this method, because it has a negative effect on the morphologic pattern of artificial teeth of complete dentures and thus should be used carefully.

Two-dimensional finite element analysis of stresses developed in the supporting tissues under complete dentures using teeth with different cusp angulations

STATEMENT OF PROBLEM

The selection of appropriate teeth for complete denture occlusion is very important for long-term success, and adequate maintenance of the residual alveolar ridge.

PURPOSE

The purpose of this study was to determine the stress generated underneath the complete denture by altering the cuspal angulations of the denture teeth.

MATERIAL AND METHODS

A two-dimensional finite element model of a coronal section of maxillary and mandibular complete dentures, mucosa and alveolar bone in the first molar region was designed. The occlusal aspect of the denture teeth was altered to make 33 degrees , 20 degrees , 0 degrees cuspal angulation. All the nodes at the bases of maxillary and mandibular alveolar bone of finite element analysis models were restrained in all directions. A functional occlusal load of 50 N was applied through the mandibular model base. To design these models and to analyse them, EMRC's NISA II finite element analysis computer software was used. In these models, the elements were selected (a, b, c, d, e, f) in the region where it was necessary to determine the stresses generated in both the maxillary and mandibular portions.

RESULTS

The results were interpreted as Von Mises stresses and were observed in pre-defined areas. The stress patterns observed within model with each type of posterior occlusion, showed unique variations as well as some similarities.

CONCLUSION

Stresses of greater magnitude were observed in cuspal teeth, 33 degrees and 20 degrees respectively, where as 0 degrees teeth showed a slightly less magnitude of stress generated.

Correlation between maximum bite force and craniofacial morphology of young adults in Indonesia

The present study was conducted to evaluate the relationship between maximum bite force and craniofacial morphology. Sixty-four Indonesian female dental students aged 19-27 years with normal occlusion served as the subjects. The Dental Prescale System was used to measure the maximum bite force using a pressure sensitive sheets while craniofacial morphology measurements were determined from conventional lateral radiograms. The antero-posterior and right-left position of the occlusal load centre (the OLC) were measured also. Stepwise multiple regression analysis was performed to evaluate the relationship between bite force and craniofacial morphology while correlation analysis was used to evaluate the antero-posterior position of the OLC related to craniofacial morphology. Fifty-five per cent of the bite force could be explained by variations in the posterior facial height, gonial angle, antero-posterior size of the maxilla, and posterior length of the cranial base. The result showed a larger bite force implies a greater posterior facial height, smaller gonial angle, larger maxilla and straighter posterior length of the cranial base. This study suggests that among Indonesians, maximum bite force could be explained by craniofacial morphology as found in Caucasians. In addition, we proposed a clinical standard of the OLC for the comprehensive evaluation of occlusion.

In vivo and in vitro evaluation of occlusal indicator sensitivity

STATEMENT OF PROBLEM

Indicators used to locate and eliminate occlusal disharmonies have not demonstrated specific sensitivity and reliability.

PURPOSE

The sensitivity and reliability of articulating papers, foils, silk strips, and T-Scan systems used as occlusal indicators were investigated. The effect of saliva on the materials also was determined.

MATERIAL AND METHODS

In the in vitro part of the study, a test model (mounted in an articulator and in a universal testing machine) was established with the use of maxillary and mandibular dentate casts. Articulating papers, foils, silk strips, and the T-Scan system were used to examine the loss of sensitivity of the recording materials after 3 consecutive strokes. The differences in the contact points of the test model determined by each of the recording materials were evaluated both in the articulator and in a universal testing machine. In the in vivo part of the study, occlusal contact recordings of 3 subjects were made before and after drying their mouths. The significance of the differences between the strokes repeated more than once was evaluated with the Friedman 2-way analysis of variance and Kruskal-Wallis tests. To examine the effect of the oral environment, the Wilcoxon matched-pairs signed-ranks test was applied. In all statistical analyses, the level of significance was alpha=.05.

RESULTS

The results demonstrated significant differences in the sensitivity of the recording materials tested (P<.001). The sensitivity of all recording materials decreased after multiple use (P<.001), and the loss of recording accuracy was significant (P<.001). All recording materials except the T-Scan were affected by the presence of saliva (P<.01).

CONCLUSION

Within the limitations of this study, the results indicated that multiple use of the recording materials tested may lead to inaccurate occlusal analysis results. It is recommended that the recording materials be used only once and that the teeth be dry during occlusal analysis.

A computerized method for evaluating balance of occlusal load

In order to undertake a quantitative evaluation of balance occlusal load, the use of the Dental Prescale System was investigated. The method uses a test sheet that undergoes a colour-developing chemical reaction, for detecting contact area, and a computerized analysis system, for evaluating the balance of occlusal load. Twenty natural dentate subjects and 10 hemimaxillectomy patients participated in the study. Each subject bit a test sheet as hard as possible for 3 s. The balance of occlusal load was expressed as a percentage of the load on the side with the lesser occlusive load (%OLR). The %OLR ranged from 39.7% to 49.4% in the natural dentate subjects, and from 0% to 31.3% in the hemimaxillectomy patients at their resection site. The patients' low %OLRs were attributed to loss of sustaining structure and subjective occlusal adjustment by clinicians. Combining technical simplicity, relatively high reproducibility, and diverse analysis capability, this system is useful for quantitative evaluation of balance of occlusal load in clinical situations.

Postoperative function after implant insertion in vascularized bone grafts in maxilla and mandible

Between 1988 and 1992, 80 Brånemark-type implants were inserted in 18 patients during reconstruction of the mandible or maxilla with vascularized iliac crest or scapula grafts with or without additional soft tissue pedicles. In these procedures, nine vascularized bone grafts were combined with a primary insertion of 32 implants and a secondary insertion of 48 implants. Twelve patients are currently wearing the implant-borne dentures. From 32 implants inserted primarily, eight could not be used for prosthodontic rehabilitation because three were lost with a graft, three were left as sleepers, and two demonstrated a lack of osseointegration. None of the implants inserted secondarily in grafts were lost. Primary implant insertion should be performed only in close cooperation with the prosthodontist and in selected cases, for example, in free-end reconstruction of the mandible with a straight graft and where a limited number of implants is needed. Although restoration of masticatory function in patients with head and neck cancer can be achieved, compared with a healthy control group, functional impairments remain. Patients subjectively favor the nonreconstructed side of the mandible or maxilla for chewing. These findings can be correlated with a postoperative follow-up investigation using a miniature force transducer and the T-scan system.