- Email: [email protected]
To the editor
READERS’ ROUND TABLE
To
THE EDITOR:
I found the article “Compressive Strengths of Conventional, Twin Foil, and All-ceramic Crowns” by Philip and Brukl (J PROSTHET DENT 5!2:215, 1984) of sound scientific methodology. However, I feel a responsibility to place studies of this nature into proper perspective for the practicing dentist. The isolation of a mechanical property such as compressive strength may not be predictive of clinical performance because it ignores a variety of other stresses that undoubtedly occur in the oral environment. As the authors point out, the compressive strength of all these materials exceeds those encountered in the oral cavity, yet it is clear that twin foil and conventional aluminous porcelain crowns are not indicated in posterior portions of the mouth because of their high failure rates. Cerestore (Johnson and Johnson Dental Products Co.. East Windsor, N.J.), on the other hand, is indicated for both anterior and posterior restorations. Nearly 5,000 anterior and posterior crowns in place for as long as 3 years showed a failure rate of only 2.6%. This compares favorably with the 2.3% failure rate for porcelain-fused-to-gold reported by Coornaert et al.’ Clearly, this suggests comparable clinical performance between Cerestore and porcelain-fused-to-gold crowns: an inference that cannot be made for any other nonmetallic system. This does not mean to suggest that testing of mechanical properties does not serve as a useful guide in certain situations. However, since ceramics are much stronger in compression than in tension,’ I feel that this single mechanical property is not indicative of clinical performance and recommend that it not be viewed as such. STEPHEN G. PASTERNACK, PH.D. VIC 1:. PRESWENT, RESEAKCI~ .AND DEVEL.OI~EN~I JOHNSON & JOHNSON Df,mn~. PRO~UTS Co. 20 LAKE DR., CN 7060 EAST WINIKOR, NJ 08520
REFERENCES 1. Coornaert J, Adriaens P, De Boever J: A long-term clinical study of porcelain-fused-to-gold restorations. J PROSTHET DENT 51:338,
2.
To
1984.
O’Brien Wj, Ryge C: An Outline of Dental Materials and Their Selection. Philadelphia, 1978, WB Saunders Co., p 185.
Bos fos LJNIVERSIT> HESRY hf. GOLDMAN SUKIOL OF (;RAW.ZTE BOSIY>Y.M:‘. 021 18
DF,NTIS
I RI
REFERENCE I.
Millstein PI,. Clark RE: Dilferential accuracy of silicone-bed) and self-curing resin interocclusal records and associated weight J PROSTHET
loss.
DENT 46~380,
1981.
Reply To THE EDITOR:
We would like to thank Dr. Millstein for his input regarding our study. We concur with his suggestion that the dimensional reliability of the interocclusal recording medium used in a specific technique has a profound effect on the overall clinical applicability of the procedure. Millstein and Clark’ studied the differential accuracy of Myo-print interocclusal records in a controlled laboratory setting. Their findings suggest that after long-term storage, Myo-print records exhibit approximately a 0.4 mm vertical and a 0.2 mm horizontal displacement of the standard dental casts. Our findings demonstrated an approximate 0.9 mm vertical (superior-inferior) and 0.4 mm horizontal displacement of the articulator transverse axis when investigating the Myo-print material in conjunction with clinical Myo-monitorinduced myocentric recording procedures. Even though the two studies measured the displacements in different manners, it can be inferred from their data that the nonmpeatability of the myocentric recording technique is due to a multifactorial mechanism that involves both the recording media and the clinical technique. YVONNE BALTHAZAR, D.D.S., M.S.
THE EDITOR:
This letter concerns the findings of a study reported in the article “Effect of Interocclusal Records on Transverse Axis Position” by Balthazar et al. (J PROSTHET DENT 52804, 1984). The authors concluded that inconsistency in myocentric registrations suggested that “Myo-monitor [Myo-tronics Research, Seattle, Wash.] stimulation had an unequal and inconsistent effect on mandibular positioning.” I would like to raise an alternate possible explanation for these conclusions, which the authors might want to consider in future research designs. The design of Balthazar et al. did not address the accuracy of the recording material. Previous work demonstrated that Myo-print (Myo-tronics Research), the recording material used in their study, was grossly inaccurate and inconsistent.’ Considering this information, a question can legitimately be raised. Instead of the technique being unreliable, it may in fact be that the technique is reliable and the 750
recording material unreliable, thus producing the inconsistent effects reported by Balthazar et al. What I am suggesting is that assumptions about the reliability of such a technique cannot be made unless the researcher separates the material from the method and cvaluates both their independent and interactive effects. PHILIP L. MILLSTEIN, D.M.D., M.S.
MARQUETTE UNIVERSITY Sr.flOOl, OF DEN’TISTRI MII.WAUKE,E, WI 53233
REFERENCE 1. Millstein PI,, Clark RE: Differential accuracy of silicone-body and self-curing resin interocclusal records and associated weight loss. J PR~STHET DENT 46:380, 1981.
To
THE
EDITOR:
I think it is necessary to comment on the article by Balthazar et al. “Effect of Interocclusal Records on Transverse Axis Position” (J PROXMET DENT 5!2:804, 1984). The statement is made that “. a repeatable maxillomandibular relationship is necessary for the dentist.” This premise is becoming more and more suspect as dentists increase their knowledge of the biomechanics of the temporomandibular joint. MAY
1985
VOLUME
53
NUMBER
5
To
THE EDITOR:
I found the article “Compressive Strengths of Conventional, Twin Foil, and All-ceramic Crowns” by Philip and Brukl (J PROSTHET DENT 5!2:215, 1984) of sound scientific methodology. However, I feel a responsibility to place studies of this nature into proper perspective for the practicing dentist. The isolation of a mechanical property such as compressive strength may not be predictive of clinical performance because it ignores a variety of other stresses that undoubtedly occur in the oral environment. As the authors point out, the compressive strength of all these materials exceeds those encountered in the oral cavity, yet it is clear that twin foil and conventional aluminous porcelain crowns are not indicated in posterior portions of the mouth because of their high failure rates. Cerestore (Johnson and Johnson Dental Products Co.. East Windsor, N.J.), on the other hand, is indicated for both anterior and posterior restorations. Nearly 5,000 anterior and posterior crowns in place for as long as 3 years showed a failure rate of only 2.6%. This compares favorably with the 2.3% failure rate for porcelain-fused-to-gold reported by Coornaert et al.’ Clearly, this suggests comparable clinical performance between Cerestore and porcelain-fused-to-gold crowns: an inference that cannot be made for any other nonmetallic system. This does not mean to suggest that testing of mechanical properties does not serve as a useful guide in certain situations. However, since ceramics are much stronger in compression than in tension,’ I feel that this single mechanical property is not indicative of clinical performance and recommend that it not be viewed as such. STEPHEN G. PASTERNACK, PH.D. VIC 1:. PRESWENT, RESEAKCI~ .AND DEVEL.OI~EN~I JOHNSON & JOHNSON Df,mn~. PRO~UTS Co. 20 LAKE DR., CN 7060 EAST WINIKOR, NJ 08520
REFERENCES 1. Coornaert J, Adriaens P, De Boever J: A long-term clinical study of porcelain-fused-to-gold restorations. J PROSTHET DENT 51:338,
2.
To
1984.
O’Brien Wj, Ryge C: An Outline of Dental Materials and Their Selection. Philadelphia, 1978, WB Saunders Co., p 185.
Bos fos LJNIVERSIT> HESRY hf. GOLDMAN SUKIOL OF (;RAW.ZTE BOSIY>Y.M:‘. 021 18
DF,NTIS
I RI
REFERENCE I.
Millstein PI,. Clark RE: Dilferential accuracy of silicone-bed) and self-curing resin interocclusal records and associated weight J PROSTHET
loss.
DENT 46~380,
1981.
Reply To THE EDITOR:
We would like to thank Dr. Millstein for his input regarding our study. We concur with his suggestion that the dimensional reliability of the interocclusal recording medium used in a specific technique has a profound effect on the overall clinical applicability of the procedure. Millstein and Clark’ studied the differential accuracy of Myo-print interocclusal records in a controlled laboratory setting. Their findings suggest that after long-term storage, Myo-print records exhibit approximately a 0.4 mm vertical and a 0.2 mm horizontal displacement of the standard dental casts. Our findings demonstrated an approximate 0.9 mm vertical (superior-inferior) and 0.4 mm horizontal displacement of the articulator transverse axis when investigating the Myo-print material in conjunction with clinical Myo-monitorinduced myocentric recording procedures. Even though the two studies measured the displacements in different manners, it can be inferred from their data that the nonmpeatability of the myocentric recording technique is due to a multifactorial mechanism that involves both the recording media and the clinical technique. YVONNE BALTHAZAR, D.D.S., M.S.
THE EDITOR:
This letter concerns the findings of a study reported in the article “Effect of Interocclusal Records on Transverse Axis Position” by Balthazar et al. (J PROSTHET DENT 52804, 1984). The authors concluded that inconsistency in myocentric registrations suggested that “Myo-monitor [Myo-tronics Research, Seattle, Wash.] stimulation had an unequal and inconsistent effect on mandibular positioning.” I would like to raise an alternate possible explanation for these conclusions, which the authors might want to consider in future research designs. The design of Balthazar et al. did not address the accuracy of the recording material. Previous work demonstrated that Myo-print (Myo-tronics Research), the recording material used in their study, was grossly inaccurate and inconsistent.’ Considering this information, a question can legitimately be raised. Instead of the technique being unreliable, it may in fact be that the technique is reliable and the 750
recording material unreliable, thus producing the inconsistent effects reported by Balthazar et al. What I am suggesting is that assumptions about the reliability of such a technique cannot be made unless the researcher separates the material from the method and cvaluates both their independent and interactive effects. PHILIP L. MILLSTEIN, D.M.D., M.S.
MARQUETTE UNIVERSITY Sr.flOOl, OF DEN’TISTRI MII.WAUKE,E, WI 53233
REFERENCE 1. Millstein PI,, Clark RE: Differential accuracy of silicone-body and self-curing resin interocclusal records and associated weight loss. J PR~STHET DENT 46:380, 1981.
To
THE
EDITOR:
I think it is necessary to comment on the article by Balthazar et al. “Effect of Interocclusal Records on Transverse Axis Position” (J PROXMET DENT 5!2:804, 1984). The statement is made that “. a repeatable maxillomandibular relationship is necessary for the dentist.” This premise is becoming more and more suspect as dentists increase their knowledge of the biomechanics of the temporomandibular joint. MAY
1985
VOLUME
53
NUMBER
5