Reliability of the evaluation of occlusal contacts in the intercuspal position

Time of day-dependent deviations in dynamic and static occlusion: A prospective clinical study

STATEMENT OF PROBLEM

The registration of dental occlusion is essential for prosthodontic treatment. However, studies on time-dependent changes of static and dynamic occlusion that may affect definitive restorations are lacking.

PURPOSE

The purpose of this prospective clinical study was to use conventional and digital occlusal registration techniques to evaluate time-dependent fluctuations in static and dynamic occlusion.

MATERIAL AND METHODS

The static and dynamic occlusion of 19 healthy individuals (14 women and 5 men with a mean ±standard deviation age of 30.8 ±4.8 years) was examined 3 times a day using occlusal foil (12-μm occlusion foil) and a digital sensor (T-Scan III). The procedure was repeated after 14 days. The statistical analysis covered all registrations referencing the first measurement point to assess occurring differences, and changes per tooth and arch were determined (α=.05). Potential influencing factors were calculated by using mixed logistic regression. Marginal probabilities were calculated considering the registration technique and the time of measurement.

RESULTS

Significant differences were found between registered occlusal patterns and the different registration techniques. Occlusal changes per maxillary dental arch were observed with static foil registration (P<.001; 98.8%), left laterotrusion foil registration (P=.001; 29.6%), right laterotrusion foil registration (P=.001; 29.6%), static sensor registration (P<.001; 20.3%), left laterotrusion sensor registration (P=.001; 71.7%), and right laterotrusion sensor registration (P=.005; 67.7%). None of the techniques showed higher probabilities of occlusal changes at a given time of day with respect to time-dependent changes.

CONCLUSIONS

The study revealed that occlusion cannot be considered constant and that the topography and intensity of the contact points vary. Circadian occlusion variance can be assumed without preferring a specific time of the day. This differentiated view of occlusion as a changing system helps to clarify the challenge of dental restorations for both the patient and the practitioner.

How to register static occlusion - Correlation of contemporary techniques

Statement of problem

A working knowledge of the analytical capacities of contemporary registration methods is essential for prosthetic treatment; however, there is a paucity of studies which coherently investigate the capabilities and limitations of the various diagnostic procedures utilized for prosthetic occlusion.

Purpose

The present prospective clinical study aimed to evaluate the similarities and differences among contemporary registration methods through comparative analysis.

Material and methods

The habitual static occlusion of 19 healthy individuals (14 women; mean age ± standard deviation, 30.8 ± 4.8 years) was analyzed 3 times a day, using shimstock foil, occlusal foil, wax registration, silicone registration, and computerized registration. The procedures were repeated after 14 days. Statistical analyses included all registrations referencing the first measurement point to assess the mean values of antagonistic contacts and the differences between these measurements. Pearson's and Kendall's correlation analyses were performed as part of the coherent mixed logistic regression model, and marginal probabilities were calculated using the registration technique and repeated measurements.

Results

Strong correlations were found among the various registration techniques. The largest effect sizes were observed among the wax, silicone, occlusion foil, and computerized registrations (r = 0.95, P < 0.001 to r = 0.62, P < 0.001), while the lowest effect sizes were found for shimstock correlations (τ = 0.41, P < 0.001 to τ = 0.27, P < 0.001). Occlusal changes per maxillary arch were observed referencing the first measurement time with wax registration (P < 0.001; 7.4%), shimstock foil (P < 0.001; 13.8%), computerized registration (P < 0.001; 20.3%), silicone registration (P = 0.009; 66.3%), and occlusion foil (P < 0.001; 98.8%). Occlusal changes per maxillary tooth were observed from the first incisor (P < 0.001; 5.7%) to the third molar (P < 0.001; 18.1%).

Conclusions

The results of the present study revealed that there are strong overall correlations among the various contemporary registration techniques. The different affinities of the techniques used to register occlusal changes, however, showed differences in the measurement techniques, which should be neither over- nor underestimated. The differential tendencies of teeth to change should be considered, even if a hypervariable system is assumed.

The association between dental arch length and oral health-related quality of life in head and neck cancer patients post-radiotherapy

AIMS

To assess the association between length of dental arch and oral health-related quality of life in head and neck cancer patients post-radiotherapy.

METHODS

Thirty head and neck cancer participants reported their oral health-related quality of life using the oral health impact profile-14 instrument and their global self-rating of general and oral health. All patients had received chemotherapy and radiotherapy. The length of dental arch was assessed in three tooth relational categories: canine-to-canine, shortened (premolars to premolars), and long (molars to molars) dental arches. Inclusion of participants for any of the three categories required verification of opposing teeth relationship with Shim Stock paper.

RESULTS

Out of 30 head and neck cancer patients, eight (27%) had a canine-to-canine dental arch, 14 (46%) had a shortened dental arch, and eight (27%) had a long dental arch. The median oral health impact profile-14 scores for participants respectively with the canine-to-canine dental arch was six (IQR = 9.25), seven (IQR = 8) for participants with shortened dental arch, and 11 (IQR = 12.5) for participants with long dental arch. There were no significant differences in oral health impact profile-14 scores between the three-tooth relational groups (Kruskal-Wallis H = 0.769, df = 2, P-value = .681). Similarly, there were no significant differences between three-tooth relational groups on the self rating of general (Chi-squared = 1.714, df = 2, P-value = .424) and oral health (Chi-squared = 1.393, df = 2, P-value = .498).

CONCLUSION

Within the limitations of this study, no association was found between the length of dental arch and oral health-related quality of life in head and neck cancer patients post-radiotherapy. Other factors such as dry mouth, oral mucositis, loss of taste, and trismus should be considered as contributory factors to reduced oral health-related quality of life in head and neck cancer patients post-radiotherapy, particularly in relation to eating difficulties.

Masticatory function after bite-raising with light-cured orthodontic band cement in healthy adults

OBJECTIVES

To evaluate the effects of bite-raising with light-cured orthodontic band cement, a method commonly used in contemporary orthodontic treatment, on masticatory function, as assessed by objective and subjective methods.

MATERIALS AND METHODS

The objective evaluation of masticatory performance and subjective evaluation of masticatory ability were performed on 30 healthy volunteers (19 females and 11 males, 22.3 ± 1.56 years) with a normal occlusion. Assessment was performed before and immediately after bite-raising. The bite-raising was done by adding light-cured orthodontic band cement (3 × 5 × 2-mm width × length × height) on the palatal cusps of the upper first molars. The masticatory performance index (MPI) was calculated from chewed test food particles using a sieving method. For the subjective evaluation, the participants performed the food intake ability (FIA) test using a questionnaire with six types of food. The correlation between the evaluation methods was determined.

RESULTS

The MPI and FIA scores of the participants were significantly reduced after bite-raising (P < .001). The MPI and FIA score reduction was not significantly different between females and males. No significant correlations were found between the changes in MPI and FIA scores.

CONCLUSIONS

Masticatory function after bite-raising with light-cured orthodontic band cement was immediately reduced, both objectively and subjectively. However, because there was no significant correlation between the objective and subjective results, an individual may not perceive his/her decreased masticatory ability to the same degree as masticatory performance was reduced. Further study is required to evaluate the long-term adaptation to this bite-raising method.

Effect of Shortened Dental Arch on Temporomandibular Joint Intra-articular Disorders

AIMS

To investigate whether a shortened dental arch (SDA), as identified by reduced posterior occlusal contacts, is a risk factor for the progression of temporomandibular joint (TMJ) intra-articular disorders (ID), as identified using imaging techniques.

METHODS

This multisite, prospective observational study with a mean follow-up period of 7.9 years had a sample of 345 participants with at least 1 temporomandibular disorder (TMD) diagnosis at baseline. SDA was defined as reduced occlusal posterior support due to lack of occlusal intercuspal contacts in the molar region on the left and/or right side. SDA was assessed at baseline and at follow-up with metalized Mylar Tape. The presence or absence of a TMJ ID and the specific TMJ ID diagnoses for baseline and follow-up images were established by a calibrated, blinded radiologist at each of three sites by using bilateral magnetic resonance imaging for soft tissue imaging for disc displacement and by bilateral multidetector computed tomography or cone beam computed tomography for hard tissue imaging for degenerative joint diseases. Wilcoxon rank sum test and linear regression analyses were used to test for an impact of SDA on TMJ ID status.

RESULTS

At baseline, TMJ ID status of either side was not significantly affected by the presence of SDA on the ipsilateral or contralateral side of the jaw (all P > .05). Furthermore, the presence or absence of SDA at baseline was also not a significant predictor for progression of the TMJ ID status between baseline and follow-up (all P > .05).

CONCLUSION

The findings of this study suggest that there is no significant effect of SDA on progression of TMJ ID.

Immediate effects of temporary bite-raising with light-cured orthodontic band cement on the electromyographic response of masticatory muscles

To assess the immediate effects of temporary bite-raising using light-cured orthodontic band cement on the superficial masseter and anterior temporalis electromyography (EMG) activity in healthy adults. Surface EMG signals were recorded bilaterally from the superficial masseter and anterior temporalis muscles of 30 volunteers with a normal occlusion, before and after having temporary bite-raising. The bite-raising was done by adding light-cured orthodontic band cement (3x5x2 mm WxLxH) on the lingual cusps of both upper first molars. The measurements were recorded (i) at rest, (ii) while clenching in centric occluding position and (iii) while chewing on an artificial test food. The EMG activity at rest and during clenching, the maximum voltage, and the duration of the identified EMG signal burst while chewing the artificial test food before and after temporary bite-raising were statistically compared using the paired t-test or the Wilcoxon signed-rank test based on the normality of the variables. The significance level was set at 5%. After temporary bite-raising, we found no significant change in integral EMG activity at rest position for the superficial masseter (mean difference (MD)=7.5 μVs) and for the anterior temporalis muscle (MD=36.8 μVs); however, the integral EMG activity during clenching was significantly reduced for the superficial masseter (MD=201.2 μVs) and for the anterior temporalis muscle (MD=151.8 μVs). During mastication, the maximum voltage of the identified burst was significantly reduced on the preferred chewing side of the superficial masseter and anterior temporalis muscles (MD=127.9 and 47.7 μV, respectively), while no significant change was found for the duration of the identified burst (MD=-34.1 and 3.4 ms, respectively) after temporary bite-raising. The results point to an altered neuromuscular behavior during clenching and chewing immediately after temporary bite-raising with light-cured orthodontic band cement. This information is relevant for orthodontists to inform their patients what will happen to their masticatory muscle activity when this bite-raising method is used.

Temporomandibular dysfunction in adult patients with myotonic dystrophy (DM1)

Myotonic muscle dystrophy is a systemic disease with early engagement of the facial muscles. Our aim was to study dysfunction of the temporomandibular system in patients with 'classic' dystrophia myotonica (DM1) and compare it with TMD patients and healthy controls. The study included 27 referred patients with DM1, 18 women and nine men, aged 30-62 years, and two matched control groups: patients with temporomandibular disorders symptoms (TMD) and healthy controls, both groups were consecutive patients. The patients answered questions regarding facial pain, jaw function and dysfunction. A clinical examination of the temporomandibular system including the occlusion was performed, and the maximum bite force and finger forces were measured. Among the DM1 patients, 33% reported difficulty biting off, and 22% had difficulty chewing, avoiding foods like meat and raw vegetables, and 37% of the DM1 patients scored their pain and discomfort as moderate to fairly severe. Their main complaints were TMJ clicking and locking, difficulty opening wide and tiredness. They had more clinical signs of dysfunction compared with the controls (P < 0·001), but no statistically significant difference to the TMD patients. The maximum bite force in DM1 patients was impaired compared to both the TMD patients and the controls (P < 0·001). Significantly more occlusal interferences were found in DM1 patients and were associated with chewing difficulties (P < 0·001). In conclusion, patients suffering from DM1 had an increased prevalence of TMD symptoms, reported impaired chewing function and had a decreased maximum bite force.

Does a face-bow lead to better occlusion in complete dentures? A randomized controlled trial: part I

OBJECTIVES

In a double-blinded randomized controlled clinical trial, the impact of face-bow registration for remounting complete dentures (CDs) on the occlusal parameters (part I) was evaluated.

MATERIALS AND METHODS

New CDs of 32 patients were duplicated and mounted after intraoral pin registration according to mean settings (group 1) and (group 2) using a face-bow (arbitrary hinge axis). The vertical dimension was reduced to the first occlusal contact point, and a bite record was fabricated in the articulator. The number of contacts and the number of teeth in contact were evaluated by a computer program (laboratory result). After randomization, half of the CDs were adjusted according to protocol of group 1 and group 2 and delivered to the patients. After 3 days (T1) and 84 days (T2), clinical static contact points and teeth in contact were counted. Contact points and teeth in contact of both groups (laboratory results) and at different moments (clinical results) were analyzed statistically with the F test and bootstrapping.

RESULTS

Laboratory: No. 2 (face-bow) showed more occlusal contact points than no. 1 (mean setting), p > 0.05. The number of teeth with at least one occlusal contact was significantly higher in no. 2 (p = 0.027). Clinic: The mean number of teeth with at least one clinical contact point was significantly higher in no. 1 (no. 1 = 7.13, no. 2 = 5.31; p = 0.042). Extent of the vertical shift poorly correlated with number of laboratory occlusal contact points (R ² = 0.017).

CONCLUSIONS

Considering the complex multistep study design, a limited number of participants, and referring to one specific arbitrary face-bow, the following conclusion could be drawn: no substantial difference by the use of the arbitrary face-bow compared to a mean setting could be determined, when changing the vertical dimension in the articulator within a remounting procedure of complete dentures.

CLINICAL RELEVANCE

Further research is necessary to determine the effects of different arbitrary face-bows on the fabrication and adaptation of removable 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.

Reliability and validity of Axis I of the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) with proposed revisions

  The research diagnostic criteria for temporomandibular disorders (RDC/TMD) have been employed internationally since 1992 for the study of temporomandibular muscle and joint disorders (TMD). This diagnostic protocol incorporates a dual system for assessment of TMD for Axis I physical diagnoses as well as Axis II psychological status and pain-related disability. Because the reliability and criterion validity of RDC/TMD had not yet been comprehensively characterised, the National Institute of Dental and Craniofacial Research funded in 2001 the most definitive research to date on the RDC/TMD as a U01 project entitled, 'Research Diagnostic Criteria: Reliability and Validity'. The results of this multi-site collaboration involving the University of Minnesota, the University of Washington, and the University at Buffalo were first reported at a pre-session workshop of the Toronto general session of the International Association of Dental Research on 2 July 2008. Summaries of five reports from this meeting are presented in this paper including: (i) reliability of RDC/TMD Axis I diagnoses based on clinical signs and symptoms; (ii) reliability of radiographic interpretations used for RDC/TMD Axis I diagnoses; (iii) reliability of self-report data used for RDC/TMD Axis I diagnoses; (iv) validity of RDC/TMD Axis I diagnoses based on clinical signs and symptoms; and (v) proposed revisions of the RDC/TMD Axis I diagnostic algorithms.

Changes in occlusal contact area during oral appliance therapy assessed on study models

OBJECTIVE

To test the hypothesis that long-term use of an oral appliance (OA) does not cause changes in the occlusal contact area (OCA).

MATERIALS AND METHODS

Baseline and follow-up treatment study models were obtained for 45 patients with obstructive sleep apnea who had been using an OA for 4 or more days/week for more than 5 years. Study models in centric occlusion, with an inserted pressure-sensitive sheet, were loaded in compression. An image scanner was used to evaluate OCA.

RESULTS

A significant change in total OCA was identified in 39 patients (86.7%): a decrease in 26 (66.7%) and an increase in 13 (33.3%) patients. Regional changes >5% were observed in >90% of patients in each of the three regions. In the molar and premolar regions, 24 (53.3%) and 27 (60.0%) of the patients showed an OCA decrease, while only 16 (35.6%) and 15 (33.3%) showed an increase. Conversely, for the anterior region, more increases (24 patients-53.3%) than decreases were identified.

CONCLUSION

The hypothesis is rejected. Long-term OA therapy resulted in dramatic changes of occlusion, suggesting that monitoring of occlusal changes is required.

Reliability of recording static and dynamic occlusal contact marks using transparent acetate sheet

STATEMENT OF PROBLEM

Inaccuracy in the transfer of information between clinician and technician regarding occlusal contacts can cause problems when fabricating indirect restorations, which can result in frustration for the dentist, technician, and patient. Few studies have considered the reproducibility of recording marked occlusal contacts.

PURPOSE

This study aimed to test the reproducibility of a quick and simple means of recording marked occlusal contacts.

MATERIAL AND METHODS

The static and dynamic occlusal contacts of 29 subjects, with no missing functional units, were marked using articulating paper. Three clinicians with varying clinical experience (3-10 years after graduation from dental school) were asked to independently record the marked occlusal contacts using a transparent acetate sheet. The results were analyzed for Kappa agreement.

RESULTS

For the static occlusion, Kappa values of agreement between pairs of examiners were 0.88, 0.86, and 0.85, respectively, all indicating "almost perfect agreement." For the dynamic occlusion, the range of Kappa agreement between pairs of examiners produced a median of 0.91, 0.88, and 0.85, respectively, indicating almost perfect strength of agreement.

CONCLUSIONS

The results suggest that marking occlusal contacts on a transparent acetate sheet provides a simple means of recording static and dynamic occlusal contacts with a high degree of reproducibility.

Comparing maximum intercuspal contacts of virtual dental patients and mounted dental casts

STATEMENT OF PROBLEM

Quantitative measures of occlusal contacts are of paramount importance in the study of chewing dysfunction. A tool is needed to identify and quantify occlusal parameters without occlusal interference caused by the technique of analysis.

PURPOSE

This laboratory simulation study compared occlusal contacts constructed from 3-dimensional images of dental casts and interocclusal records with contacts found by use of conventional methods.

MATERIALS AND METHODS

Dental casts of 10 completely dentate adults were mounted in a semi-adjustable Denar articulator. Maximum intercuspal contacts were marked on the casts using red film. Intercuspal records made with an experimental vinyl polysiloxane impression material recorded maximum intercuspation. Three-dimensional virtual models of the casts and interocclusal records were made using custom software and an optical scanner. Contacts were calculated between virtual casts aligned manually (CM), aligned with interocclusal records scanned seated on the mandibular casts (C1) or scanned independently (C2), and directly from virtual interocclusal records (IR). Sensitivity and specificity calculations used the marked contacts as the standard. Contact parameters were compared between method pairs. Statistical comparisons used analysis of variance and the Tukey-Kramer post hoc test (P=<.05).

RESULTS

Sensitivities (range 0.76-0.89) did not differ significantly among the 4 methods (P=.14); however, specificities (range 0.89-0.98) were significantly lower for IR (P=.0001). Contact parameters of methods CM, C1, and C2 differed significantly from those of method IR (P<.02). The ranking based on method pair comparisons was C2/C1 > CM/C1 = CM/C2 > C2/IR > CM/IR > C1/IR, where ">" means "closer than."

CONCLUSIONS

Within the limits of this study, occlusal contacts calculated from aligned virtual casts accurately reproduce articulator contacts.

Inter- and intra-operator reliability of the recording of occlusal contacts using 'occlusal sketch' acetate technique

OBJECTIVES

To develop a simple way of recording occlusal contacts with proven inter- and intra-operator reliability.

SETTING

Clinical skills laboratory in the University Dental Hospital of Manchester.

MATERIALS AND METHODS

The marked static occlusal contacts of 20 sets of models were recorded in a pseudo-clinical situation, by three dentists and in addition by one dentist on two occasions using a schematic representation of the dental arch - the 'occlusal sketch'.

RESULTS

The median of Kappa agreement for inter- and intra-operator reliability was almost perfect.

CONCLUSIONS

The occlusal sketch is a simple, inexpensive and easy way of recording the results of an occlusal examination using marking papers.

Relationship between the number of occlusal contacts and masticatory muscle activity in healthy young adults

The electromyographic (EMG) potentials of left and right masseter and temporalis anterior muscles were recorded in 23 healthy young adults during: 1. a 3-second maximum voluntary clench (MVC) on cotton rolls positioned on the posterior teeth (standardized recording); and 2. a 3-second MVC in intercuspal position. EMG potentials recorded in intercuspal position were standardized as a percentage of the mean potentials of the standardized recording, and the EMG muscle activity was calculated. The number of occlusal contacts in intercuspal position was assessed by using eight microm thick shim stocks. Two groups of subjects with either 1. Less than ten occlusal contacts (11 subjects with "few contacts"); or 2. At least ten occlusal contacts (12 subjects with "many contacts") were selected. The MVC muscle activity in the "few contacts" group was significantly lower than that recorded in the "many contacts" group (p<0.005). In conclusion, the number of occlusal contacts and masticatory muscular function are significantly related, at least in young adults with a sound stomatognathic apparatus.

Reliability, validity, and utility of various occlusal measurement methods and techniques

STATEMENT OF PROBLEM

The controversy continues regarding the efficacy of several commercially available devices that are used as aids in the diagnosis of occlusal abnormalities.

PURPOSE

This article reviews the reliability, validity, and utility of instruments that claim to detect occlusal interferences and abnormal vertical dimension of occlusion.

MATERIAL AND METHODS

Data, opinions, and technical information from 37 published articles were reviewed. Evidence for method reliability, validity, and utility was assessed.

RESULTS

Although occlusal contact detection devices can document the occlusal contact patterns on teeth, the basic in vivo testing of their reproducibility and validity has not been performed. Moreover, while EMG and jaw tracking systems can indeed measure jaw muscle activation and jaw position, no cost-benefit analysis of these devices has yet been conducted. One manufacturer suggests that these instruments be used in conjunction with an electrical muscle stimulation device to find a new resting jaw position that is more open vertically. This new, more open position has been inappropriately labeled as evidence of vertical dimension of occlusion over-closure.

CONCLUSION

None of the instruments reviewed can be said to be more than ancillary documentation devices and they have been inadequately tested for reliability and validity. Moreover, because scientifically acceptable disease definitions are not available for these 2 conditions, the issue of over-diagnosing becomes a substantial concern.

Digital assessment of occlusal wear patterns on occlusal stabilization splints: a pilot study

STATEMENT OF PROBLEM

If masticatory load distribution is task-dependent, then the pattern of wear on an acrylic resin occlusal splint over time may affect clinical outcome.

PURPOSE

This pilot study quantitatively assessed posterior wear after 3 months on the occlusal surfaces of maxillary stabilization splints.

MATERIAL AND METHODS

Subjects with known history of nocturnal bruxism were given heat-cured full-arch acrylic resin occlusal stabilization splints to be worn nocturnally for 3 months. Splint occlusion was adjusted at appliance delivery and was refined at the baseline session 1 to 2 weeks later. No further adjustment of the splint surface was performed during the 3-month study period. Sequential impressions of the splint occlusal surface provided epoxy resin models that were digitized and analyzed through specialized software. Changes in the digitized splint surface from baseline to 3 months allowed comparison of wear facets between splint sides and among tooth locations.

RESULTS

Splint wear was asymmetric between sides and uneven between dental locations.

CONCLUSIONS

For full coverage occlusal splints, the appliance wear phenomenon can be site specific and, if left undisturbed, may yield two extremes of high wear and a zone of low wear in-between.

Pattern of occlusal contacts in lateral positions: canine protection and group function validity in classifying guidance patterns

STATEMENT OF PROBLEM

The concept of canine protection and group function lack consistency in the definitions and examining methods, and a valid system for evaluating and classifying occlusal contact patterns has not been established.

PURPOSE

This study assessed the use of canine protection and group function in classifying occlusal guidance in the natural dentition.

MATERIAL AND METHODS

Occlusal contacts of 86 young adults were examined with shim stock in regulated lateral positions, 0.5,1,2 and 3 mm from the maximum intercuspation. The patterns of occlusal contacts varying with the lateral position were described.

RESULTS

Focusing on the working-side contact only, most contact patterns belonged to group function, and a few to canine protection. Focusing on both the working and nonworking side contacts, nearly half the contact patterns were those other than canine protection and group function and were classified into balanced occlusion.

CONCLUSION

The validity of the classification system using canine protection and group function is questionable. A new classification system of occlusal guidance is desirable.

Variation in tooth wear in young adults over a two-year period

STATEMENT OF PROBLEM

Although all the processes of loss of hard tissue are important, attrition on the occlusal surfaces commands our attention.

PURPOSE OF STUDY

The enamel wear rate of 18 young adults over 2 consecutive years was measured independently by volume loss and mean depth loss. Any significant differences in tooth wear resulting from gender and a clinical diagnosis of bruxism were identified.

MATERIAL AND METHODS

A strict protocol for dental impressions provided epoxy models, which were digitized with a null point contact stylus. AnSur software provided a complete morphologic description of changes in the wear facets.

RESULTS

The mean loss for all teeth measured was 0.04 mm3 by volume and 10.7 microns by depth for the first year.

CONCLUSIONS

These numbers were approximately doubled at 2 years of cumulative wear.