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Laboratory comparison of three occlusal registration methods for identification of induced interceptive contacts
Laboratory comparison of three occlusal registration methods for identification of induced interceptive contacts William
L. Maness, D.D.S., M.S.*
Tufts University,
School of Dental Medicine,
Boston, Mass.
This study compared
the performance of a new computerized occlusal analysis (T-Scan) system with that of Accufilm and Shimstock foil for the registration of tooth contacts on a laboratory model. Induced interceptive contacts were created on epoxy models in a mechanical closing device and the occlusal contacts were recorded for each registration method. The traditional methods were similar to the computerized analysis but the T-Scan system provided additional differential diagnostic information in force and time modes for an improved occlusal analysis. (J PROSTHET DENT 1991;65:483-7.)
T
he materials for recording occhrsal contacts are numerous and range from simple marking papers and waxes to silicone impression materials or photoelastic wafers. A computerized device recently introduced measures the timing and force of the occlusion. The performance of the registration materials and methods has been researched by many investigators in an effort to thoroughly understand the patient’s occlusion. In an in vitro study of marking paper reproducibility, Millstein’ discovered inordinate variation in the marks registered on epoxy models during repeated trials. He suggested that silicone impression materials were a more accurate method of identifying tooth contacts. Interocclusal marking materials have also been evaluated by comparing their reproducibility using various marking paper types. Schelb et a1.2studied inked registration materials and confirmed variation in color, substrate material, and thickness, and concluded that the thinner Mylar film (DuPont Co., Wilmington, Del.) materials produced the most reliable marks. Their research was corroborated by Halperin et al3 Photo-occlusion introduced a new data source by measuring relative tooth contact intensity with a photoelastic wafer under polarized light. In a clinical comparison of the reproducibility of photo-occlusion and an inked marking material, Gazit et al.4 concluded that neither method was highly reproducible, and that the photoelastic wafer enhanced posterior contact intensity while diminishing anterior contacts. The T-Scan system (Tekscan Inc., Boston, Mass.), a computerized device with an electronic sensor, is another means of evaluating tooth contacts6
*AssociateClinical Professor,Department of Graduateand Postgraduate Prosthodontics. 10/l/24171
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
This study compared the performance of the T-Scan system with two conventional registration methods: Accufihn material (Parkell Products, Farmingdale, N.Y.) and Shimstock foil (Almore International, Portland, Ore.) to identify induced in vitro interceptive contacts.
MATEWAL
AND METBODS
A mechanical closing device was constructed to occlude two epoxy models reproducibly during the closing motion (Fig. 1). Two springs exerted a constant force of 20 pounds at the in&al pin and a damping pot was inserted to control the closing speed of the articulator. Once the device was released, the instrument closed at a constant speed and force, creating a repeatable motion with reproducible tooth contacts. Posterior and anterior tooth contacts were induced on the epoxy models, creating two groups of contacts.
Posterior
interceptive
contacts
A posterior interceptive contact was created on the mesiolingual cusp of the maxillary right first molar by a piece of 75 Frn copper foil cemented directly on the cusp tip (Fig. 2). When the mounted casts were occluded within the closing device, a substantial premature contact was produced on the mesiolingual cusp of the maxillary first molar.
Anterior
interceptive
contacts
The anterior interceptive Contacts were created by a shim placed in the anterior segment of the cast with several layers of copper foil beneath the mounting ring and the upper bow of the articulator. When the mechanical device was closed, only the anterior segment of the dental arches contacted.
Tooth contact evaluation The tooth contacts were evaluated with Accufilm and 8 wrn Shimstock materials and recorded by tooth num-
483
MANESS
Casts
Fig. 1. Diagram of mechanical model for closing epoxy casts.
Fig. 2. The posterior interceptive contact with 75 pm foil
Fig. 3. Mechanical closing device and holder for sensor
on right first molars with anterior contacts from maxillary right to maxillary left first premolar as marked with Accufilm material (except maxillary central incisors).
handle with sensor inserted in epoxy models.
ber. The Accufilm and Shimstock methods were combined to identify the actual tooth contacts on the epoxy models and the data were considered the standard measure. The tooth contacts were then evaluated by the T-Scan system in the following manner. The T-Scan system sensor handle was secured in a holding device to prevent movement and a sensor was inserted (Fig. 3). The epoxy models were closed on the sensor and four replicates with I5 sensors were repeated in both time and force modes for 60 trials each. The tooth contacts were recorded by tooth number.
RESULTS The data for the comparison of Accufilm and Shimstock materials versus the T-Scan system were analyzed for agreement with the Kappa test, including sensitivity and
484
specificity values.6 The results are summarized in Tables I and II. Kappa, varying from zero to one, represents the degree of diagnostic agreement between two measurement systems. Only the diagonal of a bivariate table of diagnostic statements was included in the calculations because false positive and false negative were excluded. Percent sensitivity is equal to 100 multiplied by the ratio of true positives to the sum of true positives plus false negatives. Percent specificity is equal to 100 multiplied by the ratio of true negatives to the sum of true negatives plus false positives.
Posterior
interceptive
contacts
Accufilm and Shimstock were used to identify the actual interceptive contacts. Both materials identified the maxillary right first and second molars as the predominant contacts although the induced interceptive contact was placed
APRIL
1991
VOLUME
65
NUMBER
4
THREE
OCCLUSAL
REGISTRATION
METHODS
Fig. 4. T-Scan system force mode illustrating posterior induced interceptive contact with highest force on right first molar.
6. T-Scan system force mode with force columns identifying induced interceptive contacts on maxillary right first premolar and canine.
Table I. Kappa test agreements between Accufilm/Shimstock materials and T-Scan system registration methods for induced interceptive contacts
Table II. Sensitivity and specificity values comparing Accufilm/Shimstock materials versus T-Scan system registration methods for induced interceptive contacts
Test
(T-Scan vs. actual)
% Agreement
Posterior contacts Time 2/3 Time 3 Force 3 Anterior contacts Time 5/6 Force 516
Kappa
value
p Level
100.0 96.2 97.6
1.000 0.696 0.816
95.1 99.3
0.607 0.946
on the first molar. Despite other contacts, the Accufilm registered the most conspicuous mark on the maxillary right first molar and the foil was torn on removal from both teeth. The T-Scan in time mode agreed with the conventional methods by identifying contact surfaces on the maxillary right first and second molars as the predominant contacts in 100% of the trials. The T-Scan also identified the induced contact on the maxillary right first molar as the initial contact in 96% of the experimental trials. Sensitivity and specificity values were highly reliable for the maxillary right first and second molars as the predominant contacts without false positives (both 100% ) and for the maxillary right first molar as the initial contact (71.6% and 97.9%) respectively). When the posterior contacts were examined in force mode, the T-Scan system identified the induced contact on the maxillary right first molar (Fig. 4) as the greatest force in 97 % of the trials. Sensitivity and specificity values were 80% and 98.9 % , respectively.
Anterior
interceptive
contacts
Accufilm and foil identified the maxillary right first premolar and right canine as the most interceptive contacts by
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Fig.
Test (T-Scan
vs.
actual)
Posterior contacts Time 2/3 Time 3 Force 3 Anterior contacts Time 5/6 Force 5/6
Sensitivity
(%)
Specificity
(%)
100.0 71.6 80.0
100.0 97.9 98.9
63.3 95.0
97.3 99.6
the most distinct markings and resistance to withdrawal, respectively. The T-Scan system in time mode agreed with Accufilm material and foil in identifying the initial contact surfaces on the maxillary right first premolar and canine in 95% of the trials. However, when force mode was used to identify tooth contacts, the greatest forces were measured on the maxillary right first premolar and canine 99% of the time (Figs. 5 and 6). Sensitivity and specificity values for time mode versus actual contacts were 63.3 % and 97.9 % , respectively, and the force mode versus actual tooth contacts were 95 % and 99.6%.
DISCUSSION Marking materials identify tooth contacts by leaving deposits of ink on the contact surfaces with significant surfaces having the intense marks. This method has a tendency of produce false-positive data.2 Conversely, the Shimstock material rarely produces false-positive information and, therefore, improves the confidence of the dentist if used with inked registration materials. To improve the identification of the actual tooth con-
485
MANES8
rial and foil improved the accuracy of the test for actual laboratory tooth contacts.
T-Scan system evaluation Sixty trials for both force and time modes were recorded for the T-Scan system. The tooth contacts identified were tabulated and the data analyzed for agreement with the Accufilm and Shimstock materials.
Posterior
Fig. 6. T-Scan system force mode with tooth contacts identified on maxillary right first molar and canine and maxillary left canine with greatest force on right premolar and canine.
tacts, Accufilm and Shimstock materials were combined as a single test because of complimentary properties.
Marking
paper evaluation
The marks created by closing the casts were identified and their intensity (size and darkness) were recorded. Substantial marks were noted on the mesiolingual cusp of the maxillary right first molar and in the central fossa of the maxillary right second molar with lighter marks observed on the molars and premolars of the contralateral side. The marks were more apparent on the maxillary right first and second molars with the induced prematurity on the first molar registering a large contact. The anterior prematurities were more difficult to discern with the Accufilm material, which marked all anterior teeth from the maxillary right first premolar to the maxillary left first premolar except the left central incisor. On closer examination, the maxillary right first premolar and canine had the most conspicuous tooth contacts but the maxillary left canine was also prominent.
Shimstock
evaluation
Checking the contacts with the 8 pm foil revealed that the maxillary right first and second molars produced sufficient resistance to withdrawal to tear the foil. The foil was removed with minimal resistance on the remaining teeth, indicating lack of actual contact. In the anterior experimental group, Shimstock material offered the greatest resistance to withdrawal on the maxillary right first premolar and canine with the other teeth exhibiting limited resistance to the foil. The Shimstock material successfully identified the actual teeth in contact, but was nonspecific regarding the actual contact position. The combination of Accufihn mate-
486
interceptive
contacts,
force mode
The posterior induced contact was identified by the TScan system in force mode on the maxillary right first molar as the greatest force in 97 % of the trials (Kappa test). This finding is critical with respect to the Accufilm and Shimstock materials data. These materials did not differentiate between the two contacts and left the dentist without an objective method of discerning between teeth. The high sensitivity of 80% also supported the ability of the T-Scan system to identify the induced contact as the highest force without recording false positive force levels on the other teeth during the 60 trials (specificity 98.9%).
Posterior
interceptive
contacts,
time mode
The T-Scan system demonstrated 100% agreement in identifying the maxillary right first and second molars as the initial contact, with the first molar identified as the actual first contact in 96% of the trials. The sensitivity and specificity values for comparing actual contacts with T-Scan system contacts in time mode were 100% for the maxillary right first and second molars. This indicated that other tooth contacts were not identified by the T-Scan system during this test and that it was devoid of false positives. The ability of the T-Scan system to discriminate between tooth contacts using relative force and time values infers desirable clinical application. The T-Scan system would improve the understanding of the dynamics of relative force and time values for occlusion.
Anterior
interceptive
contacts
The anterior induced contacts were arduous to discern with all methods because they were numerous with only minute differences in the degree of prematurity. Measurements of agreement (Kappa test) for actual tooth contacts in the maxillary right first premolar and canine were 95% in time mode and 99% in force mode. However, sensitivity values indicated the time mode was less reliable than force mode in detecting actual anterior contacts (63 % and 95 % , respectively). Nevertheless, both modes recorded limited false recordings as reflected by the specificity values (97.3% and 99.6%). The low sensitivity value for time reflects the more simultaneous nature of the anterior contacts and emphasizes that when tooth contacts are numerous and simulta-
APRIL
1991
VOLUME
06
NUMBER
4
TRREE OCCLUSAL REGISTRATION METHODS
neous, force is an accurate measure of clinical discrepancies in occlusion. These findings were consistent with clinical experience since teeth that develop pathologic conditions commonly suffer from excessive occlusal loading.’
CONCLUSIONS This study compared the T-Scan system in time and force modes with Accufllm and Shimstock materials for identifying induced interceptive contacts in a laboratory model system. The conclusions drawn were: 1. Accufilm or Shimstock materials did not adequately ensure actual contact identification and so were combined to exploit complementary properties. 2. Accufilm material recorded false-positive contacts on the epoxy model more particularly in the anterior experimental group. 3. T-Scan system time and force modes agreed with the conventional methods for identifying actual contacts in both the anterior and posterior experimental groups. 4. T-Scan system force mode was the most reliable indicator of interceptive contacts, expecially if contacts were simultaneous and numerous.
5. T-Scan system force mode provided a differential agnostic criterion with substantial clinical relevance occlusion.
difor
REFERENCES Millstein PL. An evaluation of occlusal contact marking indicators: a descriptive qualitative method. Quint lnternat 1983;143813-7. Schelb E, Kaiser D, Brukl C. Thickness and marking characteristics of occlusal registration strips. J PROSTH~TDENT 1988;54:122-6. Halperin G, Halperin A, Norling B. Thickness, strength, and plastic deformation of occlusal registration strips. J PROSTRRT DENT 1982;48:575-8. Gaxit D, Fitxig S, Lieberman M. Reproducibility of occlusal marking techniques. J PROSTHETDENT 1986$8565-9. Maness W, Benjamin M, Podoloff R, Bobick A, Golden R. Computerized occlusal analysis: a new technology. Quint Intemat 1987;4:287-92. Fleiss F. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley & Sons, 1981;217-8. Mohl N, Zarb G, Carlsson G, Rugh J. A textbook of occlusion. Chicago: Quintessence Publishing Co, 1988;229-30. Reprint requests to: DR. WILLIAML. MANESS 237 LEWISWHARF BOST~JN, MA 02110
Microhardness of class II composite resin restorations with different matrices and light positions Benjamin T. Kays, D.D.S.,+ William D. Sneed, D.M.D.,** and Douglas B. Nuckles, D.D.S.*+* Medical University of South Carolina, College of Dental Medicine, Charleston, S.C. The degree of polymerization, determined by surface hardness, has been related to the gingival marginal adaptation of posterior composite resin restorations. Poor marginal adaptation results from marginal leakage and failure of the restoration. This study compared the degree of polymerization, measured by microhardness, of a microfilled composite resin placed by use of different matrices. The effect on polymerization with the curing light in two positions was also evaluated. (J PROSTHET DENT 1991;05:487-90.)
T
he two major limitations of composite resins for posterior restorations have been microleakage from poor gingival marginal adaptation and inadequate resistance to wear. An unacceptable margin reduces the life of the restoration and may also affect the vitality of the tooth. Thus, the marginal adaptation of composite resins remains suspect.1-3
*Clinical Assistant Professor, Department of Operative Dentistry. **Professor and Chairman, Department of Operative Dentistry. ***Professor and Research Coordinator, Department of Operative Dentistry. 10/l/24172
TEE JOURNAL OF PROSTHETIC DENTISTRY
Although composite resins have been placed in posterior teeth since the 19’7Os,they have been considered unsuccessful. In former clinical studies, ocehrsal wear of the material was not one of the measured variables but was noted in clinical trials. In those early studies, the margimd adaptation was only evaluated on the occlusal surfaces by use of an explorer.4-6 Recently, there has been heightened concern about gingival marginal adaptation of class II composite resin restorations.3-7 With the introduction of light-cured composite resins, there has been revised interest in the quality of polymerization and renewed concern about marginal adaptation.*-” However, because manipulation of materials and
487
L. Maness, D.D.S., M.S.*
Tufts University,
School of Dental Medicine,
Boston, Mass.
This study compared
the performance of a new computerized occlusal analysis (T-Scan) system with that of Accufilm and Shimstock foil for the registration of tooth contacts on a laboratory model. Induced interceptive contacts were created on epoxy models in a mechanical closing device and the occlusal contacts were recorded for each registration method. The traditional methods were similar to the computerized analysis but the T-Scan system provided additional differential diagnostic information in force and time modes for an improved occlusal analysis. (J PROSTHET DENT 1991;65:483-7.)
T
he materials for recording occhrsal contacts are numerous and range from simple marking papers and waxes to silicone impression materials or photoelastic wafers. A computerized device recently introduced measures the timing and force of the occlusion. The performance of the registration materials and methods has been researched by many investigators in an effort to thoroughly understand the patient’s occlusion. In an in vitro study of marking paper reproducibility, Millstein’ discovered inordinate variation in the marks registered on epoxy models during repeated trials. He suggested that silicone impression materials were a more accurate method of identifying tooth contacts. Interocclusal marking materials have also been evaluated by comparing their reproducibility using various marking paper types. Schelb et a1.2studied inked registration materials and confirmed variation in color, substrate material, and thickness, and concluded that the thinner Mylar film (DuPont Co., Wilmington, Del.) materials produced the most reliable marks. Their research was corroborated by Halperin et al3 Photo-occlusion introduced a new data source by measuring relative tooth contact intensity with a photoelastic wafer under polarized light. In a clinical comparison of the reproducibility of photo-occlusion and an inked marking material, Gazit et al.4 concluded that neither method was highly reproducible, and that the photoelastic wafer enhanced posterior contact intensity while diminishing anterior contacts. The T-Scan system (Tekscan Inc., Boston, Mass.), a computerized device with an electronic sensor, is another means of evaluating tooth contacts6
*AssociateClinical Professor,Department of Graduateand Postgraduate Prosthodontics. 10/l/24171
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
This study compared the performance of the T-Scan system with two conventional registration methods: Accufihn material (Parkell Products, Farmingdale, N.Y.) and Shimstock foil (Almore International, Portland, Ore.) to identify induced in vitro interceptive contacts.
MATEWAL
AND METBODS
A mechanical closing device was constructed to occlude two epoxy models reproducibly during the closing motion (Fig. 1). Two springs exerted a constant force of 20 pounds at the in&al pin and a damping pot was inserted to control the closing speed of the articulator. Once the device was released, the instrument closed at a constant speed and force, creating a repeatable motion with reproducible tooth contacts. Posterior and anterior tooth contacts were induced on the epoxy models, creating two groups of contacts.
Posterior
interceptive
contacts
A posterior interceptive contact was created on the mesiolingual cusp of the maxillary right first molar by a piece of 75 Frn copper foil cemented directly on the cusp tip (Fig. 2). When the mounted casts were occluded within the closing device, a substantial premature contact was produced on the mesiolingual cusp of the maxillary first molar.
Anterior
interceptive
contacts
The anterior interceptive Contacts were created by a shim placed in the anterior segment of the cast with several layers of copper foil beneath the mounting ring and the upper bow of the articulator. When the mechanical device was closed, only the anterior segment of the dental arches contacted.
Tooth contact evaluation The tooth contacts were evaluated with Accufilm and 8 wrn Shimstock materials and recorded by tooth num-
483
MANESS
Casts
Fig. 1. Diagram of mechanical model for closing epoxy casts.
Fig. 2. The posterior interceptive contact with 75 pm foil
Fig. 3. Mechanical closing device and holder for sensor
on right first molars with anterior contacts from maxillary right to maxillary left first premolar as marked with Accufilm material (except maxillary central incisors).
handle with sensor inserted in epoxy models.
ber. The Accufilm and Shimstock methods were combined to identify the actual tooth contacts on the epoxy models and the data were considered the standard measure. The tooth contacts were then evaluated by the T-Scan system in the following manner. The T-Scan system sensor handle was secured in a holding device to prevent movement and a sensor was inserted (Fig. 3). The epoxy models were closed on the sensor and four replicates with I5 sensors were repeated in both time and force modes for 60 trials each. The tooth contacts were recorded by tooth number.
RESULTS The data for the comparison of Accufilm and Shimstock materials versus the T-Scan system were analyzed for agreement with the Kappa test, including sensitivity and
484
specificity values.6 The results are summarized in Tables I and II. Kappa, varying from zero to one, represents the degree of diagnostic agreement between two measurement systems. Only the diagonal of a bivariate table of diagnostic statements was included in the calculations because false positive and false negative were excluded. Percent sensitivity is equal to 100 multiplied by the ratio of true positives to the sum of true positives plus false negatives. Percent specificity is equal to 100 multiplied by the ratio of true negatives to the sum of true negatives plus false positives.
Posterior
interceptive
contacts
Accufilm and Shimstock were used to identify the actual interceptive contacts. Both materials identified the maxillary right first and second molars as the predominant contacts although the induced interceptive contact was placed
APRIL
1991
VOLUME
65
NUMBER
4
THREE
OCCLUSAL
REGISTRATION
METHODS
Fig. 4. T-Scan system force mode illustrating posterior induced interceptive contact with highest force on right first molar.
6. T-Scan system force mode with force columns identifying induced interceptive contacts on maxillary right first premolar and canine.
Table I. Kappa test agreements between Accufilm/Shimstock materials and T-Scan system registration methods for induced interceptive contacts
Table II. Sensitivity and specificity values comparing Accufilm/Shimstock materials versus T-Scan system registration methods for induced interceptive contacts
Test
(T-Scan vs. actual)
% Agreement
Posterior contacts Time 2/3 Time 3 Force 3 Anterior contacts Time 5/6 Force 516
Kappa
value
p Level
100.0 96.2 97.6
1.000 0.696 0.816
95.1 99.3
0.607 0.946
on the first molar. Despite other contacts, the Accufilm registered the most conspicuous mark on the maxillary right first molar and the foil was torn on removal from both teeth. The T-Scan in time mode agreed with the conventional methods by identifying contact surfaces on the maxillary right first and second molars as the predominant contacts in 100% of the trials. The T-Scan also identified the induced contact on the maxillary right first molar as the initial contact in 96% of the experimental trials. Sensitivity and specificity values were highly reliable for the maxillary right first and second molars as the predominant contacts without false positives (both 100% ) and for the maxillary right first molar as the initial contact (71.6% and 97.9%) respectively). When the posterior contacts were examined in force mode, the T-Scan system identified the induced contact on the maxillary right first molar (Fig. 4) as the greatest force in 97 % of the trials. Sensitivity and specificity values were 80% and 98.9 % , respectively.
Anterior
interceptive
contacts
Accufilm and foil identified the maxillary right first premolar and right canine as the most interceptive contacts by
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Fig.
Test (T-Scan
vs.
actual)
Posterior contacts Time 2/3 Time 3 Force 3 Anterior contacts Time 5/6 Force 5/6
Sensitivity
(%)
Specificity
(%)
100.0 71.6 80.0
100.0 97.9 98.9
63.3 95.0
97.3 99.6
the most distinct markings and resistance to withdrawal, respectively. The T-Scan system in time mode agreed with Accufilm material and foil in identifying the initial contact surfaces on the maxillary right first premolar and canine in 95% of the trials. However, when force mode was used to identify tooth contacts, the greatest forces were measured on the maxillary right first premolar and canine 99% of the time (Figs. 5 and 6). Sensitivity and specificity values for time mode versus actual contacts were 63.3 % and 97.9 % , respectively, and the force mode versus actual tooth contacts were 95 % and 99.6%.
DISCUSSION Marking materials identify tooth contacts by leaving deposits of ink on the contact surfaces with significant surfaces having the intense marks. This method has a tendency of produce false-positive data.2 Conversely, the Shimstock material rarely produces false-positive information and, therefore, improves the confidence of the dentist if used with inked registration materials. To improve the identification of the actual tooth con-
485
MANES8
rial and foil improved the accuracy of the test for actual laboratory tooth contacts.
T-Scan system evaluation Sixty trials for both force and time modes were recorded for the T-Scan system. The tooth contacts identified were tabulated and the data analyzed for agreement with the Accufilm and Shimstock materials.
Posterior
Fig. 6. T-Scan system force mode with tooth contacts identified on maxillary right first molar and canine and maxillary left canine with greatest force on right premolar and canine.
tacts, Accufilm and Shimstock materials were combined as a single test because of complimentary properties.
Marking
paper evaluation
The marks created by closing the casts were identified and their intensity (size and darkness) were recorded. Substantial marks were noted on the mesiolingual cusp of the maxillary right first molar and in the central fossa of the maxillary right second molar with lighter marks observed on the molars and premolars of the contralateral side. The marks were more apparent on the maxillary right first and second molars with the induced prematurity on the first molar registering a large contact. The anterior prematurities were more difficult to discern with the Accufilm material, which marked all anterior teeth from the maxillary right first premolar to the maxillary left first premolar except the left central incisor. On closer examination, the maxillary right first premolar and canine had the most conspicuous tooth contacts but the maxillary left canine was also prominent.
Shimstock
evaluation
Checking the contacts with the 8 pm foil revealed that the maxillary right first and second molars produced sufficient resistance to withdrawal to tear the foil. The foil was removed with minimal resistance on the remaining teeth, indicating lack of actual contact. In the anterior experimental group, Shimstock material offered the greatest resistance to withdrawal on the maxillary right first premolar and canine with the other teeth exhibiting limited resistance to the foil. The Shimstock material successfully identified the actual teeth in contact, but was nonspecific regarding the actual contact position. The combination of Accufihn mate-
486
interceptive
contacts,
force mode
The posterior induced contact was identified by the TScan system in force mode on the maxillary right first molar as the greatest force in 97 % of the trials (Kappa test). This finding is critical with respect to the Accufilm and Shimstock materials data. These materials did not differentiate between the two contacts and left the dentist without an objective method of discerning between teeth. The high sensitivity of 80% also supported the ability of the T-Scan system to identify the induced contact as the highest force without recording false positive force levels on the other teeth during the 60 trials (specificity 98.9%).
Posterior
interceptive
contacts,
time mode
The T-Scan system demonstrated 100% agreement in identifying the maxillary right first and second molars as the initial contact, with the first molar identified as the actual first contact in 96% of the trials. The sensitivity and specificity values for comparing actual contacts with T-Scan system contacts in time mode were 100% for the maxillary right first and second molars. This indicated that other tooth contacts were not identified by the T-Scan system during this test and that it was devoid of false positives. The ability of the T-Scan system to discriminate between tooth contacts using relative force and time values infers desirable clinical application. The T-Scan system would improve the understanding of the dynamics of relative force and time values for occlusion.
Anterior
interceptive
contacts
The anterior induced contacts were arduous to discern with all methods because they were numerous with only minute differences in the degree of prematurity. Measurements of agreement (Kappa test) for actual tooth contacts in the maxillary right first premolar and canine were 95% in time mode and 99% in force mode. However, sensitivity values indicated the time mode was less reliable than force mode in detecting actual anterior contacts (63 % and 95 % , respectively). Nevertheless, both modes recorded limited false recordings as reflected by the specificity values (97.3% and 99.6%). The low sensitivity value for time reflects the more simultaneous nature of the anterior contacts and emphasizes that when tooth contacts are numerous and simulta-
APRIL
1991
VOLUME
06
NUMBER
4
TRREE OCCLUSAL REGISTRATION METHODS
neous, force is an accurate measure of clinical discrepancies in occlusion. These findings were consistent with clinical experience since teeth that develop pathologic conditions commonly suffer from excessive occlusal loading.’
CONCLUSIONS This study compared the T-Scan system in time and force modes with Accufllm and Shimstock materials for identifying induced interceptive contacts in a laboratory model system. The conclusions drawn were: 1. Accufilm or Shimstock materials did not adequately ensure actual contact identification and so were combined to exploit complementary properties. 2. Accufilm material recorded false-positive contacts on the epoxy model more particularly in the anterior experimental group. 3. T-Scan system time and force modes agreed with the conventional methods for identifying actual contacts in both the anterior and posterior experimental groups. 4. T-Scan system force mode was the most reliable indicator of interceptive contacts, expecially if contacts were simultaneous and numerous.
5. T-Scan system force mode provided a differential agnostic criterion with substantial clinical relevance occlusion.
difor
REFERENCES Millstein PL. An evaluation of occlusal contact marking indicators: a descriptive qualitative method. Quint lnternat 1983;143813-7. Schelb E, Kaiser D, Brukl C. Thickness and marking characteristics of occlusal registration strips. J PROSTH~TDENT 1988;54:122-6. Halperin G, Halperin A, Norling B. Thickness, strength, and plastic deformation of occlusal registration strips. J PROSTRRT DENT 1982;48:575-8. Gaxit D, Fitxig S, Lieberman M. Reproducibility of occlusal marking techniques. J PROSTHETDENT 1986$8565-9. Maness W, Benjamin M, Podoloff R, Bobick A, Golden R. Computerized occlusal analysis: a new technology. Quint Intemat 1987;4:287-92. Fleiss F. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley & Sons, 1981;217-8. Mohl N, Zarb G, Carlsson G, Rugh J. A textbook of occlusion. Chicago: Quintessence Publishing Co, 1988;229-30. Reprint requests to: DR. WILLIAML. MANESS 237 LEWISWHARF BOST~JN, MA 02110
Microhardness of class II composite resin restorations with different matrices and light positions Benjamin T. Kays, D.D.S.,+ William D. Sneed, D.M.D.,** and Douglas B. Nuckles, D.D.S.*+* Medical University of South Carolina, College of Dental Medicine, Charleston, S.C. The degree of polymerization, determined by surface hardness, has been related to the gingival marginal adaptation of posterior composite resin restorations. Poor marginal adaptation results from marginal leakage and failure of the restoration. This study compared the degree of polymerization, measured by microhardness, of a microfilled composite resin placed by use of different matrices. The effect on polymerization with the curing light in two positions was also evaluated. (J PROSTHET DENT 1991;05:487-90.)
T
he two major limitations of composite resins for posterior restorations have been microleakage from poor gingival marginal adaptation and inadequate resistance to wear. An unacceptable margin reduces the life of the restoration and may also affect the vitality of the tooth. Thus, the marginal adaptation of composite resins remains suspect.1-3
*Clinical Assistant Professor, Department of Operative Dentistry. **Professor and Chairman, Department of Operative Dentistry. ***Professor and Research Coordinator, Department of Operative Dentistry. 10/l/24172
TEE JOURNAL OF PROSTHETIC DENTISTRY
Although composite resins have been placed in posterior teeth since the 19’7Os,they have been considered unsuccessful. In former clinical studies, ocehrsal wear of the material was not one of the measured variables but was noted in clinical trials. In those early studies, the margimd adaptation was only evaluated on the occlusal surfaces by use of an explorer.4-6 Recently, there has been heightened concern about gingival marginal adaptation of class II composite resin restorations.3-7 With the introduction of light-cured composite resins, there has been revised interest in the quality of polymerization and renewed concern about marginal adaptation.*-” However, because manipulation of materials and
487