J. Dent. 1990;
18: 107-l
107
12
Microleakage in restorations with glass ionomer liners after thermocycling* C. J. Arcoria,
B. A. Vitasek*,
J. P. DeWald and M. J. Wagnert
Department of Operative Dentistry, * Car&h School of Dental Hygiene and tDepartment College of Dentistry, Dallas, Texas, USA
of Biochemistry,
Baylor
ABSTRACT The purpose of this study was to compare microleakage around two types of restorations lined with polyalkenoate (glass ionomer) cements after thermocycling. Preparations were made in 48 molars to a diameter and depth of 2.0 mm. Halfof the preparations were lined with glass ionomer, and the remainder were not lined. Dental amalgam or glass ionomer restorative material was placed and the amalgams were left unburnished and unpolished. Selected restorations were thermocycled 625 times between 4°C and 50°C. Teeth were immersed in 0.5 per cent methylene blue solution, sectioned and visually scored for microleakage at X 100 magnification. Data analysis indicated significant differences in microleakage because of: thermocycling
(x2 = 103.38, d.f. = 19, 2P < 0.0004); presence of glass ionomer liners (x2 = 53.28, d.f. = 19. 2P < 0.0001); and type of restorative material (x2 = 103.44, d.f. = 19.2P < 0.0004). The use of a glass ionomer liner significantly reduced
microleakage
in both amalgam
KEY WORDS:
Polyalkenoate
J. Dent. 1990; 1989)
18: 107-I
Correspondence Dentistry, 3302
and glass ionomer
(glass ionomer) cements, 12 (Received 4 October
restorations
1989;
reviewed
INTRODUCTION Discounting inaccuracies with material placement and improper design of cavity preparations, the absence of microleakage in operative restorations is directly related to the presence of leakage-inhibiting materials. Additionally, the presence of a bond or seal of the restorative material to tooth structure may reduce the occurrence of microleakage (Douglas, 1989; Ibsen et al., 1989). Research has shown that dental amalgam has a significant leakage potential in the short term, more so than many other types of direct restorative materials (Fanian et al., 1983). As a consequence, investigators have searched for alternatives to dental amalgam (McLean. 1984). In the quest to develop microleakage-resistant, conservative restorative materials, researchers have discovered that the polyalkenoate (glass ionomer) cements have many of the characteristics needed to satisfy these criteria (Mount and Makinson, 1978). Glass ionomer cements are *The findings of this study were presented at the 67th General Session of the IADR, Dublin, Ireland, 1989. Ltd.
to thermocycling.
Liners, Microleakage
should be addressed to: Dr C. J. Arcoria, Department Gaston Avenue, Dallas, TX 75246, USA.
0 1990 Butterworth & i‘o (Pubhshers) 0300-5712/90/020107-06
when subjected
3 November
of Operative
1989;
accepted 8 December
Dentistry,
Baylor College of
used as substitutes for dental amalgam and composite resins in non-stress-bearing areas because of their adhesion to tooth structure (Coury et al.. 1982; Powis et al., 1982) and capacity to release fluoride into adjacent enamel and dentine (Swartz et al., 1984). Unfortunately. glass ionomer cements do not possess a great amount of compressive and tensile strength (McLean, 1980). In fact, research has indicated that these materials will exhibit brittle failure at forces far less than those that would cause failure in dental amalgam (Tjan and Morgan, 1988; Arcoria et al., 1989). Moreover, the material exhibits poor wear resistance when utilized as a permanent restorative material (McLean, 1980; Ngo et al.. 1986). Recently, investigators have studied the application of glass ionomer cements as bases and liners beneath various restorations (McLean et al., 1985; Hinoura et al.. 1987). The rationale for using these materials as liners is that they can be easily manipulated into cavity preparations and provide a release of fluoride thereby reducing the risk of recurrent caries (Maldonado et al., 1978). Moreover, these liners can be acid etched to increase the
108
J. Dent. 1990;
18: No. 2
Table 1. Number
of dye penetration
Restorative material
Treatment liner placement
Tytin Tytin
G.I. liner G.I. liner
Tytin Ketac-fil Ketac-fil Ketac-fil Ketac-fil
No liner G.I. liner G.I. liner No liner No liner
scores for each treatment
group
Penetration Storage treatment
score *
0
I
2
3
4
Thermocycled Non-cycled
0
0
1
:
0 0
Thermocycled Non-cycled Thermocycled Non-cycled Thermocycled Non-cycled
:, 0
;2
A 0 0
; 0 0
:0 2 0 0 3
0 4 0 0 2 3
E 0 0 4 0
n = 6 for each group. *Penetration score: 0, no leakage; 1, superficial leakage; 2, leakage to the DEJ; 3, leakage into the dentine; 4, leakage to the pulpal wall.
bond between a composite resin restorative material and the glass ionomer cement (Garcia-Godoy et al., 1988). thereby increasing the retention and resistance to microleakage (Fayyad and Shortall, 1987). On the other hand, conflicting research has indicated that glass ionomer liners may not reduce microleakage and that these ‘sandwich’ restorations are more prone to failure (Welsh and Hembree, 1985: Crim and Shay, 1987; Scherer et al., 1989). Obviously, further research is necessary to resolve this issue. Although glass ionomer cements have been used very successfully as a supportive material instead of the principal restoration, they may be the material of choice as the primary restorative material when a patient has a higher than normal risk for caries (Brandau et al.. 1984). For instance, it has been shown that many geriatric patients with low rates of salivary flow (due to specific chronic disorders and their medications) exhibit a severe caries problem (Massler, 1976). Dental amalgam and composite resin fail to prevent a recurrence of decay in these patients. It has been demonstrated that glass ionomer restorations, despite their disadvantages regarding wear resistance and compressive strength, can be used as a viable alternative to amalgam or composite because of their low marginal leakage rates and their capacity to release fluoride. thereby decreasing the occurrence of recurrent caries (Knibbs, 1987; Olsen et al., 1989). To study microleakage between glass ionomer cements and amalgams in the laboratory, a method is needed for simulating the ageing of the restoration on an accelerated basis (Lloyd et al.. 1978). Thermocycling causes marginal deterioration of all types of restorative materials at a much faster rate than seen in appropriate controls (Andrews and Hembree. 1980; Yates et al., 1980). The technique utilizes a repeated low and high temperature stress cycle over a range of 4-50°C for dwell times of approximately 30 s (Gottlieb et al.. 1985). Research has indicated that the thermocycling model will hasten the process of microleakage in vitro, thereby inducing failure of the restoration (Crim and Garcia-Godoy. 1987; Crim and Shay, 1987: Darbyshire et al.. 1988: Davis et al.. 1989).
The objective of this study was to compare microleakage in preparations lined with glass ionomer lining cement and restored with glass ionomer restorative cement or dental amalgam after thermocycling.
MATERIALS
AND METHODS
Forty-eight intact human extracted mandibular molars free of adherent tissue were used in the study. Immediately following extraction, the teeth were stored in deionized water-glycerin-isopropanol-3 per cent hydrogen peroxide solution, 50 : 20: 20: 10 (Arcoria et al., 1988, 1989) throughout the experiment. A cavity preparation measuring 2.0 mm in depth and diameter was made with a 170 fissure bur (Brasseler, Savannah. GA USA) in the middle third of the buccal aspect of each tooth. An enamel hatchet (Thompson Dental Mfg., Missoula, MT, USA) was used to create a 90” cavosurface angle without a bevel. The entire dentinal surface of each preparation in onehalf of the samples (n = 24) was coated with a thin layer (approximately 1.0 mm) of Shofu glass ionomer lining cement (Shofu Dental Products Inc., Kyoto, Japan) using a ball-tipped applicator (Thompson Dental Mfg.). The depth of the thin layer of glass ionomer lining cement was later verified between 0.85 and 1.20 mm after the restorations were sectioned. The lining cement was permitted to cure for 4 min in a controlled environment chamber of 37°C and 50 per cent humidity. The dentine did not receive a pretreatment with any solution prior to glass ionomer placement (Darbyshire et al., 1988). In addition, surface conditioners were not applied to the cured glass ionomer liners prior to final restorative material placement. All 48 teeth were then restored with either dental amalgam (Tytin, Sybron/Kerr, Romulus, MI, USA) or glass ionomer restorative cement (Ketac-til, ESPE/Premier Dental, Norristown, PA USA). The glass ionomer material was mixed in a Vari-Mix amalgamator (L. D. Caulk, Milford, DE. USA) for 10 s at medium-2 speed and then syringed into the cavity preparation. The material was adapted to the margins of the preparation with a D. E. Woodson no. 3 plastic instrument (Thompson Dental
Arcoria
Pulpal Wall
enamel
\
I
et al.: Microleakage
\
with
dentine /
glass-ionomer
liners
109
enamel \ external tooth surface /
......................... ......................... :::::.:::::::::::::::::::::: .............................. ........................ ...................................................................... ...................................................................... ...................................................................... .................................................... ...................................................... :::::::::::::::: ...................................................................... ...................................................................... ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ;;::,;:;;;;;;.::::;;;;; :::::;;:::;;;::::::;::::::::::::::: ..................... ............................................................. :::::::::::::::::::: ................................................................................. ............................ ......... ............ ........... ................... .... ................................ ........... ............. ........... ......
/
............................................................................... ...............................................................................
1
I
dentine I
fig. 7. Cross-section of molar with glass ionomer amalgam or Ketac-fil restoration.
I
liner and
Mfg.). A mylar matrix strip (Healthco Dental Supply, Dallas, TX. USA) was applied to the restoration to ensure a smooth external surface with close adaptation of the restorative material to the margins. After the material completely cured (7 min after placement in the cavity preparations). each glass ionomer restoration was protected from air dehydration and subsequent water imbibition by removal of the matrix strip and immediate application of one coat of glass ionomer varnish (Ketac-Varnish, ESPE-Premier). No surface finishing procedures were performed on any of the glass ionomer restorative samples. The ionomer restorations were then examined under a light-diffraction microscope (Wild Photoautomat MPS 45. Heerbrugg, SWZ) at X 100 magnification to ensure close adaptation of the glass ionomer cement to the margins, without voids or discrepancies. Restorations not satisfying this criterion were rejected and replaced with new sample teeth containing restorations that were considered acceptable for testing. Restored specimens were placed in a 37 “C and 100 per cent humidity chamber for 36 h before thermocycling. The glass ionomer varnish was removed from each glass ionomer final restoration prior to thermocycling with a no. 23 dental explorer (Hu Friedy. Chicago, IL, USA). As before, no surface finishing procedures were performed on the glass ionomer restorations. The dental amalgam was mixed in an amalgamator (Vari-Mix, L.D. Caulk) for 8 s at medium-2 speed and placed in the cavity preparations with a D.E. amalgam carrier (American Dental Mfg., Missoula. MT, USA). The material was condensed with an amalgam condenser of tip diameter 0.7-1.0 mm (Thompson Dental Mfg.) for 10 s and carved with a discoid-cleoid (3.0 mm bladed) amalgam carver (Thompson Dental Mfg.) flush to the margins. Amalgam excess was removed from the margins
Fig. 2. Degree of dye penetration. 0, no leakage; 1, superficial leakage (confined to the enamel only); 2, leakage to the DEJ; 3, leakage into dentine; 4, leakage to the pulpal wall of the preparation.
without burnishing or polishing the material. The amalgam restorations were also placed in 100 per cent humidity at 37°C for 36 h prior to thermocycling. Table I depicts the placement of samples in each experimental group, and Fig. I displays a cross-section diagram of a typical restoration with a glass ionomer liner. One-half of the samples from each restoration category were thermocycled in deionized water. with a temperature differential of46”C (4-50°C) for 625 cycles. Dwell time in each temperature bath was 30 s, with a transfer time of 10 s. After thermocycling, each specimen was coated to within 1.0 mm of the margin of the restoration with two applications of a toluene-based clear nail polish (Del Laboratories, Farmingdale, NY, USA). Only the crown of each specimen was immersed in a 0.5 per cent aqueous methylene blue dye solution (Ricca Chemical Co.. Arlington, TX. USA) for 6 h (Spangberg et al., 1989). After dye immersion, the teeth were rinsed with deionized water for 1 min and sectioned buccolingually through each restoration with a slow-speed diamond saw (Buehler, Ltd. Lake Bluff. IL. USA). Sectioned samples of the restorations were then examined at X 100 magnification with a light-diffraction microscope (Wild Photoautomat MPS 45) to determine the amount of dye penetration at the margins. Microleakage was visually scored according to the following scale: 0 = no leakage, 1 = superficial leakage (into the enamel only). 2 = leakage to the dentinoenamel junction. 3 = leakage into the dentine. and 4 = leakage to the pulpal wall (Fig. 2).
RESULTS The dye penetration scores for each treatment group are displayed in Table 1. The dental amalgam (Tytin) and glass ionomer restorative (Ketac-fil) restorations are
110
J. Dent. 1990;
18: No. 2
Table II. Significance U test (2P < 0.05)
of differences
in microleakage
scores
Variable
Comparison *
type type type type
using the Mann-Whitney
P value
TC-L-T NT-L-T TC- N L-T NT-N L-T
vs. vs. vs. vs.
TC-L-K NT-L-K TC-NL-K NT-NL-K
Restoration Restoration Restoration Restoration
T-L-TC T-N L-TC K- L-TC K-N L-TC
vs. vs. vs. vs.
T-L-NT T-N L-NT K-L-NT K-N L-NT
Thermocycling Thermocycling Thermocycling Thermocycling
0.0006 < 0.0001 0.0027 0.00 13
T-TC- L T-NT-L K-TC- L K-NT-L
vs. vs. vs. vs.
T-TC-N L T-NT-NL K-TC-N L K-NT-NL
Liner Liner Liner Liner
0.0002 0.0 104 0.00 13 < 0.0001
presence presence presence presence
0.0006 0.002 7 NS NS
*Comparison legend: T, dental amalgam (Tytin); K, glass ionomer restorative cement (Ketac-fil); TC, thermocycling; NT, no thermocycling; L, glass ionomer liner (Shofu); NL, noglass ionomer liner. NS, P value was not significant.
divided into glass ionomer-lined and unlined samples and further subdivided into thermocycled and nonthermocycled groups. Contingency tables were constructed from the data in Table Z and tested for statistical significance with x2 analysis, using 2P < 0.05 as the level of significance. For each leakage class, the scores of samples treated a specific way (e.g. thermocycled) were compared with the scores of the control samples (e.g. non-thermocycled). The MannWhitney U test was utilized to detect differences between individual treatment groups at the 2P < 0.05 level. TableZZ depicts the significance of differences in microleakage scores using this latter analysis. Significant differences in microleakage scores were found for each of the three treatment conditions: (1) type of restorative material (x2 = 103.44, d.f. = 19,2P < 0.0004), (2) thermocycling(x2 = 103.38, d.f. = 19,2P < 0.0004), and (3) presence or absence of the glass ionomer liner (x2 = 53.28, d.f. = 19, 2P < 0.0001). In addition, the Mann-Whitney U test indicated that microleakage around restorations that contained the glass ionomer lining cement was significantly different from that in samples in which no liner was placed (2P < 0.0001). Significant differences regarding restoration types were apparent when dental amalgam/lined/thermocycled samples ;were compared with the glass ionomer restored/ lined/thermocycled samples (2P < 0.0006); and also when dental amalgam/lined/non-thermocycled specimens were compared with the glass ionomer restored/lined/ non-thermocycled specimens (2P < 0.0027). Differences between unlined samples of dental amalgam (Tytin) and glass ionomer (Ketac-El) restorations, irrespective of thermocycling, were not found to be significant.
DISCUSSION The purpose of this study was to investigate the effects of glass ionomer liner placement in dental amalgam (Tytin)
vs. glass ionomer (Ketac-fil) restorations. In addition, the effect of thermocycling was evaluated to determine whether artificial ageing (thermocycling) caused significantly more microleakage with either restorative material or because of the presence of a glass ionomer liner. The use of methylene blue to detect marginal gaps between a tooth-restoration interface has been widely documented (Spangberg et al., 1989). The aqueous solution of methylene blue (0.5 per cent) allows for both the uptake of the dye within the matrix of the glass ionomer restoration and for penetration of the dye because of marginal deterioration. Dye tracers are much smaller than the 0.5 pm diameter that oral bacteria require to travel between the tooth-resin interface (Krell and Madison, 1985; Douglas, 1989). Therefore, the dye can be used as a stringent test of marginal microleakage. Previous research has demonstrated that the use of a glass ionomer liner was effective in reducing microleakage (Hinoura et al., 1987; Garcia-Godoy et al., 1988). Because of the tendency for operative restorations to exhibit microleakage, glass ionomer liners were proposed to lessen this potential for failure (McLean et al. 1985; Fayyad and Shortall, 1987). The results of this study also demonstrated that a glass ionomer liner reduced the occurrence of microleakage in amalgam restorations. In addition, a thermocycling model was utilized to ascertain the effects of accelerated ageing on the leakageinhibiting capacity of glass ionomer lining cements, irrespective of restoration type. The effect of thermocycling caused a significant difference in microleakage for all groups, when compared to the corresponding nonthermocycled controls. However, thermocycling did not cause the extreme effects associated with an ageing model perhaps because the duration of total cycling time (625 cycles) was not as long as in other studies (Lloyd et al., 1978; Davis et al., 1989; Arcoria et al., 1989). Alternatively, separate studies did indicate that short-term thermocycling could induce a significant amount of microleakage in
Arcoria et al.: Microleakage
composite resin and amalgam restorations (Yates et al., 1980; Gottlieb et& 1985: Crim and Shay, 1987; Schereret al., 1989). The presence of the glass ionomer liner was extremely important in reducing microleakage in either type of restorative material. If microleakage at the margins of restorations is a result of the lack of bond (seal) between the tooth substance and restorative material, then the microleakage should have been most apparent in the groups in which no liner was used. i.e. with direct physical contact between tooth substance and material. However, in this study. these differences were not statistically significant. Instead, the differences between restorative materials became significant only when a glass ionomer liner was interposed between tooth and restoration. This difference persisted in both the thermocycled and nonthermocycled groups. Whether this effect was due to the use of the type of liner chosen for this study or to the use of any type of liner needs further investigation. Glass ionomer cement bonds significantly less to dentine than to enamel (Coury et al., 1982). The difference in the inorganic composition of enamel vs. dentine accounts for this occurrence (higher proportion of calcium ions in enamel). As a result, the dentine bond to glass ionomer should be established before the enamel bond of the final restorative material is formed so as not to disturb the dentine-liner interface (Hinoura et al.. 1987). Understandably, the glass ionomer-lined composite restorations have demonstrated a detachment of the liner from the walls of the cavity preparation (Crim and Shay. 1987: Chan and Swift, 1989). The bond of composite resin to enamel is greater than the bond of the glass ionomer liner to dentine. Admittedly, a composite resin restoration will undergo polymerization shrinkage and/or imbibition of water (Bowen et al.. 1982) to a greater degree than a glass ionomer restorative material (Feilzer et al., 1988). However, glass ionomer cements also have the potential to exhibit shrinkage (although at a much slower rate than composite resins) and to absorb a great amount of water unless properly protected during the curing process. Consequently, the purpose of using a glass ionomer liner in this study was to wet the dentine with a material that acted as a primer for the final restoration. In addition, the liner was completely polymerized and bonded to the dentine before the glass ionomer restorative material was bonded to the liner and to the enamel. Although the glass ionomer restorative material (Ketac-fil) does not have a particularly high degree of viscosity, it adapted better to a preparation if a less viscous liner (Shofu) of similar composition acted as a primer for the final restoration. Observation of glass ionomer restorations devoid of a liner saw marginal gaps at the dentinoenamel junction with the dye penetrating to the deep portions of the preparation. This was particularly evident with the thermocycled samples. However, the non-thermocycled glass ionomer restorations without liners also displayed these marginal gaps at the dentino-enamel junction with resultant microleakage. This study demonstrated that the
with
glass-ionomer
liners
111
use of a glass ionomer liner in both dental amalgam and glass ionomer restorations was successful in reducing microleakage. Furthermore, the difference in microleakage between dental amalgam and glass ionomer restorations was significant only when a glass ionomer liner was present.
Acknowledgement This study was supported in part by Baylor Dentistry Research Funds.
College
of
References J. T. and Hembree J. H. (1980) Marginal leakage of amalgam alloys with high content of copper: a laboratory study. Oper. Dent. 5, 7-10. Arcoria C. J., DeWald J. P., Moody C. R. et al. (1988) Effects of thermocycling on amalgam and alloy-glass ionomer cores luted to cast gold crowns. Denr. Mater. 4, 155-157. Andrews
Arcoria C. J.. DeWald J. P.. Moody C. R. et al. (1989) A comparative study of amalgam and alloy-glass ionomer cores. J. Oral Rehabil. 16, 301-307. Bowen R. L., Rapson J. E. and Dickson G. (1982) Hardening shrinkage and hygroscopic expansion of composite resins. J. Dent Res. 61, 654-658. Brandau H. E., Ziermiecki T. L. and Charbeneau G. T. (1984) Restoration of cervical contours on non-prepared teeth using glass ionomer cement: a four and one-half year study. J. Am. Dent. Assoc. 108,782-783. Chan K. C. and Swift E. J. (1989) Leakage of chemical and light-cured basing materials. J. Prosthet. Dent. 62, 408-411. Coury T. L., Miranda F. J., Willer R. D. et al. (1982) Adhesiveness of glass ionomer cement to enamel and dentin: a laboratory study. Oper. Dent. 7,2-7. Crim G. A. and Garcia-Godoy F. (1987) Microleakage: the effect of storage and cyclic duration. J. Prosthet. Dent. 57, 574-576. Crim G. A. and Shay J. S. (1987) Microleakage pattern of a resin-veneered glass-ionomer cavity liner. J. Prosthet. Dent. 58, 273-276. Darbyshire P. A., Messer L. B. and Douglas W. H. (1988) Microleakage in class II composite restorations bonded to dentin using thermal and load cycling. 1 Dent. Res. 67, 585-587. Davis E. L., Joynt R. B., Wieczkowski G. et al. (1989) Bond durability between dentinal bonding agents and tooth structure. J. Prosthet. Dent. 62, 253-256. Douglas W. H. (1989) Clinical status of dentine bonding agents. J. Dent. 17,209-215. Fanian F., Hadavi F. and Asgar K. (1983) Marginal leakage of dental amalgam Oper. Dent. 8, l-7. Fayyad M. A and Shortall A. C. C. (1987) Microleakage of dentine-bonded posterior composite restorations. J. Dent. 15, 67-72. Feilzer A. J., DeGee A J. and Davidson (3. L. (1988) Curing contraction of composite restoratives and glass ionomer cements. J. Prosthet Dent. 59, 297-300. Garcia-Godoy F., Draheim R. N.. Titus H. W. et al. (1988) Microleakage of composite restorations with etched and non-etched glass ionomer bases. Am. J. Dent. 1, 159-162. Gottlieb E. W.. Retief D. H. and Bradley E. L. (1985) Microleakage of conventional and high-copper amalgam restorations. J. Prosthet. Dent 53, 355-361. Hinoura K.. Moore B. K. and Phillips R. W. (1987) Tensile bond strength between glass ionomer cements and composite resins. J. Am. Dent. Assoc. 114, 167-172.
112
J. Dent.
1990;
18: No. 2
Ibsen R., Ouellet D. and Strassler H. (1989) Clinically successful dentin and enamel bonding. Am. J. Dent. 2, 125-131. Knibbs P. J. (1987) A clinical report on the use of a glass ionomer cement to restore cervical margin lesions. J. Oral Rehabil. 14, 105-109. Krell K. V. and Madison S. (1985) Comparison of apical leakage in teeth obturated with a calcium phosphate cement or grossman’s cement using lateral condensation. J. Endodont. 11, 336-339. Lloyd B. A, McGinley M. B. and Brown W. S. (1978) Thermal stress in teeth. J. Dent Res. 51, 461-467. Maldonado A., Swartz M. L. and Phillips R. W. (1978) An in vitro study of certain properties of glass ionomer cement. J. Am. Dent. Assoc. 96, 785-791. Massler M. (1976) Oral problems in the aging patient. J. Indiana Dent. Assoc. 55, 13-15. McLean J. W. (1980) Aesthetics in restorative dentistry. Br. Dent. J. 149, 368-373. McLean J. W. (1984) Alternatives to amalgam alloys: I. Br. Dent. J. 157,432-433. McLean J. W., Prosser H. J. and Wilson A. D. (1985) The use of glass ionomer cements in bonding composite resins to dentin. Br. Dent J. 158,410-414. Mount G. J. and Makinson 0. F. (1978) Clinical characteristics of glass ionomer cement. Br. Dent. J. 145, 67-71.
Ngo H., Earl A. and Mount G. J. (1986) Glass ionomer cements: a 12-month evaluation. J. Pro&et. Dent. 55, 203-205. Olsen B. T., Garcia-Godoy F., Marshall T. D. et al. (1989) Fluoride release from glass ionomer-lined amalgam restorations. Am. J. Dent. 2, 89-91. Powis D. R., Folleras T., Merson S. A. et al. (1982) Improved adhesion of a glass ionomer cement to dentin and enamel. J. Dent. Res. 61, 1416-1422. Scherer W.. Kaim J., Lippman N. et al. (1989) Microleakage of three glass ionomer cement bases. Am. J. Dent. 2, 61-63. Spangberg L. S., Aciemo T. G. and Cha B. Y. (1989) Influence of entrapped air on the accuracy of leakage studies using dye penetration methods. J. Endodont. 15, 548-551. Swartz M. L.. Philips R. W. and Clark H. E. (1984) Long term fluoride release from glass ionomer cements. J. Dent. Res. 63, 158-160. Tjan A. H. and Morgan D. S. (1988) Metal-reinforced glass ionomers: their flexural and bond strength to tooth substrates. J. Pro&et. Dent. 59, 137-141. Welsh E. L. and Hembree J. H. (1985) Microleakage at the gingival wall with four class V anterior restorative materials. J. Prosthet. Dent. 54, 370-372. Yates J. L., Murray G. A. and Hembree J. H. (1980) Cavity varnishes applied over insulating bases: effect on microleakage. Oper. Dent. 5,43-46.
Book Reviews Diagnostic Picture Tests in Dentistry. P. J. Lamey and M. A. 0. Lewis. Pp. 128. 1988. Wolfe Medical. Softback, f 7.50. ‘An old soldier I perceive’ said Sherlock ‘and very recently discharged’, remarked ‘served in India, I see’ ‘and a non-commissioned Officer’ ‘Royal Artillery, I fancy’ said Sherlock. ‘And a widower’. ‘But with a child’ ‘children my dear boy, children’.
London,
the brother
Few dentists can match Holmes’ powers of observation and deduction and this little book should prove invaluable to them in preparing for the slide projection test of the FDS, or similar postgraduate, or even undergraduate, examinations. In 2 12, almost uniformly excellent clinical photographs, radiographs and photomicrographs, with questions and answers, Drs Lamey and Lewis provide an entertaining and informative quiz, successfully covering the major disciplines in general dentistry at just the right level. Equally, you can use it for a personal selfassessment, which certainly exposed the deficiencies in my own knowledge. Inspired guess-work is needed to identify the Paget’s disease depicted in figures 160 and 161 and only the nocturnal could decipher the murky radiograph in figure 8. In the next edition, an accompanying history and a better photomicrograph could be provided for the case of lichen planus shown in figure 51, but I suppose that minor injustices of this kind are, in themselves, all part of the average FDS examination. This book can be strongly recommended for such candidates, keen undergraduates and to any dentists feeling dangerously complacent about their general level of knowledge. D. M. Walker
A Guide to Dental Radiography, 3rd edition. Rita A. Mason. Pp. 226. 1988. Guildford, Butterworths. Softback, f 15.95. This third edition of A Guide to Dental Radiography has grown to 13 chapters and 226 pages. The book gives a complete description of all intraoral and extraoral techniques. For intraoral radiography paralleling, bisecting angle and occlusal film techniques are described in detail and the advantages of the ‘long cone’ technique stated. In addition to the chapters on extraoral techniques there are separate chapters describing radiography of the facial bones (including temporomandibular joint radiography), salivary glands and dental radiography for children. There is an extensive chapter on panoramic radiography describing the theoretical background to what the author terms ‘dental panoramic tomography’. Practical descriptions are given of how to operate panoramic machines and the effects of incorrect positioning of the patient are carefully illustrated. The chapters on radiation protection, factors affecting the radiograph, processing and image quality assurance all give the important background on how to diminish the damaging effects of X-rays but at the same time achieve a high quality radiograph. Different ways of keeping the dose to the patient as low as possible are emphasized within the description of each radiographic technique and there are many practical hints of use to the practitioner, in particular, some excellent summaries of advantages and disadvantages of the techniques described. The book is easy to read and the illustrations are carefully selected and reproduced to a very high quality. The guide is especially useful to the dental practitioner, but can also be highly recommended as a textbook for students of dental radiography. A. Petersson
18: 107-l
107
12
Microleakage in restorations with glass ionomer liners after thermocycling* C. J. Arcoria,
B. A. Vitasek*,
J. P. DeWald and M. J. Wagnert
Department of Operative Dentistry, * Car&h School of Dental Hygiene and tDepartment College of Dentistry, Dallas, Texas, USA
of Biochemistry,
Baylor
ABSTRACT The purpose of this study was to compare microleakage around two types of restorations lined with polyalkenoate (glass ionomer) cements after thermocycling. Preparations were made in 48 molars to a diameter and depth of 2.0 mm. Halfof the preparations were lined with glass ionomer, and the remainder were not lined. Dental amalgam or glass ionomer restorative material was placed and the amalgams were left unburnished and unpolished. Selected restorations were thermocycled 625 times between 4°C and 50°C. Teeth were immersed in 0.5 per cent methylene blue solution, sectioned and visually scored for microleakage at X 100 magnification. Data analysis indicated significant differences in microleakage because of: thermocycling
(x2 = 103.38, d.f. = 19, 2P < 0.0004); presence of glass ionomer liners (x2 = 53.28, d.f. = 19. 2P < 0.0001); and type of restorative material (x2 = 103.44, d.f. = 19.2P < 0.0004). The use of a glass ionomer liner significantly reduced
microleakage
in both amalgam
KEY WORDS:
Polyalkenoate
J. Dent. 1990; 1989)
18: 107-I
Correspondence Dentistry, 3302
and glass ionomer
(glass ionomer) cements, 12 (Received 4 October
restorations
1989;
reviewed
INTRODUCTION Discounting inaccuracies with material placement and improper design of cavity preparations, the absence of microleakage in operative restorations is directly related to the presence of leakage-inhibiting materials. Additionally, the presence of a bond or seal of the restorative material to tooth structure may reduce the occurrence of microleakage (Douglas, 1989; Ibsen et al., 1989). Research has shown that dental amalgam has a significant leakage potential in the short term, more so than many other types of direct restorative materials (Fanian et al., 1983). As a consequence, investigators have searched for alternatives to dental amalgam (McLean. 1984). In the quest to develop microleakage-resistant, conservative restorative materials, researchers have discovered that the polyalkenoate (glass ionomer) cements have many of the characteristics needed to satisfy these criteria (Mount and Makinson, 1978). Glass ionomer cements are *The findings of this study were presented at the 67th General Session of the IADR, Dublin, Ireland, 1989. Ltd.
to thermocycling.
Liners, Microleakage
should be addressed to: Dr C. J. Arcoria, Department Gaston Avenue, Dallas, TX 75246, USA.
0 1990 Butterworth & i‘o (Pubhshers) 0300-5712/90/020107-06
when subjected
3 November
of Operative
1989;
accepted 8 December
Dentistry,
Baylor College of
used as substitutes for dental amalgam and composite resins in non-stress-bearing areas because of their adhesion to tooth structure (Coury et al.. 1982; Powis et al., 1982) and capacity to release fluoride into adjacent enamel and dentine (Swartz et al., 1984). Unfortunately. glass ionomer cements do not possess a great amount of compressive and tensile strength (McLean, 1980). In fact, research has indicated that these materials will exhibit brittle failure at forces far less than those that would cause failure in dental amalgam (Tjan and Morgan, 1988; Arcoria et al., 1989). Moreover, the material exhibits poor wear resistance when utilized as a permanent restorative material (McLean, 1980; Ngo et al.. 1986). Recently, investigators have studied the application of glass ionomer cements as bases and liners beneath various restorations (McLean et al., 1985; Hinoura et al.. 1987). The rationale for using these materials as liners is that they can be easily manipulated into cavity preparations and provide a release of fluoride thereby reducing the risk of recurrent caries (Maldonado et al., 1978). Moreover, these liners can be acid etched to increase the
108
J. Dent. 1990;
18: No. 2
Table 1. Number
of dye penetration
Restorative material
Treatment liner placement
Tytin Tytin
G.I. liner G.I. liner
Tytin Ketac-fil Ketac-fil Ketac-fil Ketac-fil
No liner G.I. liner G.I. liner No liner No liner
scores for each treatment
group
Penetration Storage treatment
score *
0
I
2
3
4
Thermocycled Non-cycled
0
0
1
:
0 0
Thermocycled Non-cycled Thermocycled Non-cycled Thermocycled Non-cycled
:, 0
;2
A 0 0
; 0 0
:0 2 0 0 3
0 4 0 0 2 3
E 0 0 4 0
n = 6 for each group. *Penetration score: 0, no leakage; 1, superficial leakage; 2, leakage to the DEJ; 3, leakage into the dentine; 4, leakage to the pulpal wall.
bond between a composite resin restorative material and the glass ionomer cement (Garcia-Godoy et al., 1988). thereby increasing the retention and resistance to microleakage (Fayyad and Shortall, 1987). On the other hand, conflicting research has indicated that glass ionomer liners may not reduce microleakage and that these ‘sandwich’ restorations are more prone to failure (Welsh and Hembree, 1985: Crim and Shay, 1987; Scherer et al., 1989). Obviously, further research is necessary to resolve this issue. Although glass ionomer cements have been used very successfully as a supportive material instead of the principal restoration, they may be the material of choice as the primary restorative material when a patient has a higher than normal risk for caries (Brandau et al.. 1984). For instance, it has been shown that many geriatric patients with low rates of salivary flow (due to specific chronic disorders and their medications) exhibit a severe caries problem (Massler, 1976). Dental amalgam and composite resin fail to prevent a recurrence of decay in these patients. It has been demonstrated that glass ionomer restorations, despite their disadvantages regarding wear resistance and compressive strength, can be used as a viable alternative to amalgam or composite because of their low marginal leakage rates and their capacity to release fluoride. thereby decreasing the occurrence of recurrent caries (Knibbs, 1987; Olsen et al., 1989). To study microleakage between glass ionomer cements and amalgams in the laboratory, a method is needed for simulating the ageing of the restoration on an accelerated basis (Lloyd et al.. 1978). Thermocycling causes marginal deterioration of all types of restorative materials at a much faster rate than seen in appropriate controls (Andrews and Hembree. 1980; Yates et al., 1980). The technique utilizes a repeated low and high temperature stress cycle over a range of 4-50°C for dwell times of approximately 30 s (Gottlieb et al.. 1985). Research has indicated that the thermocycling model will hasten the process of microleakage in vitro, thereby inducing failure of the restoration (Crim and Garcia-Godoy. 1987; Crim and Shay, 1987: Darbyshire et al.. 1988: Davis et al.. 1989).
The objective of this study was to compare microleakage in preparations lined with glass ionomer lining cement and restored with glass ionomer restorative cement or dental amalgam after thermocycling.
MATERIALS
AND METHODS
Forty-eight intact human extracted mandibular molars free of adherent tissue were used in the study. Immediately following extraction, the teeth were stored in deionized water-glycerin-isopropanol-3 per cent hydrogen peroxide solution, 50 : 20: 20: 10 (Arcoria et al., 1988, 1989) throughout the experiment. A cavity preparation measuring 2.0 mm in depth and diameter was made with a 170 fissure bur (Brasseler, Savannah. GA USA) in the middle third of the buccal aspect of each tooth. An enamel hatchet (Thompson Dental Mfg., Missoula, MT, USA) was used to create a 90” cavosurface angle without a bevel. The entire dentinal surface of each preparation in onehalf of the samples (n = 24) was coated with a thin layer (approximately 1.0 mm) of Shofu glass ionomer lining cement (Shofu Dental Products Inc., Kyoto, Japan) using a ball-tipped applicator (Thompson Dental Mfg.). The depth of the thin layer of glass ionomer lining cement was later verified between 0.85 and 1.20 mm after the restorations were sectioned. The lining cement was permitted to cure for 4 min in a controlled environment chamber of 37°C and 50 per cent humidity. The dentine did not receive a pretreatment with any solution prior to glass ionomer placement (Darbyshire et al., 1988). In addition, surface conditioners were not applied to the cured glass ionomer liners prior to final restorative material placement. All 48 teeth were then restored with either dental amalgam (Tytin, Sybron/Kerr, Romulus, MI, USA) or glass ionomer restorative cement (Ketac-til, ESPE/Premier Dental, Norristown, PA USA). The glass ionomer material was mixed in a Vari-Mix amalgamator (L. D. Caulk, Milford, DE. USA) for 10 s at medium-2 speed and then syringed into the cavity preparation. The material was adapted to the margins of the preparation with a D. E. Woodson no. 3 plastic instrument (Thompson Dental
Arcoria
Pulpal Wall
enamel
\
I
et al.: Microleakage
\
with
dentine /
glass-ionomer
liners
109
enamel \ external tooth surface /
......................... ......................... :::::.:::::::::::::::::::::: .............................. ........................ ...................................................................... ...................................................................... ...................................................................... .................................................... ...................................................... :::::::::::::::: ...................................................................... ...................................................................... ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ................................................................................. ;;::,;:;;;;;;.::::;;;;; :::::;;:::;;;::::::;::::::::::::::: ..................... ............................................................. :::::::::::::::::::: ................................................................................. ............................ ......... ............ ........... ................... .... ................................ ........... ............. ........... ......
/
............................................................................... ...............................................................................
1
I
dentine I
fig. 7. Cross-section of molar with glass ionomer amalgam or Ketac-fil restoration.
I
liner and
Mfg.). A mylar matrix strip (Healthco Dental Supply, Dallas, TX. USA) was applied to the restoration to ensure a smooth external surface with close adaptation of the restorative material to the margins. After the material completely cured (7 min after placement in the cavity preparations). each glass ionomer restoration was protected from air dehydration and subsequent water imbibition by removal of the matrix strip and immediate application of one coat of glass ionomer varnish (Ketac-Varnish, ESPE-Premier). No surface finishing procedures were performed on any of the glass ionomer restorative samples. The ionomer restorations were then examined under a light-diffraction microscope (Wild Photoautomat MPS 45. Heerbrugg, SWZ) at X 100 magnification to ensure close adaptation of the glass ionomer cement to the margins, without voids or discrepancies. Restorations not satisfying this criterion were rejected and replaced with new sample teeth containing restorations that were considered acceptable for testing. Restored specimens were placed in a 37 “C and 100 per cent humidity chamber for 36 h before thermocycling. The glass ionomer varnish was removed from each glass ionomer final restoration prior to thermocycling with a no. 23 dental explorer (Hu Friedy. Chicago, IL, USA). As before, no surface finishing procedures were performed on the glass ionomer restorations. The dental amalgam was mixed in an amalgamator (Vari-Mix, L.D. Caulk) for 8 s at medium-2 speed and placed in the cavity preparations with a D.E. amalgam carrier (American Dental Mfg., Missoula. MT, USA). The material was condensed with an amalgam condenser of tip diameter 0.7-1.0 mm (Thompson Dental Mfg.) for 10 s and carved with a discoid-cleoid (3.0 mm bladed) amalgam carver (Thompson Dental Mfg.) flush to the margins. Amalgam excess was removed from the margins
Fig. 2. Degree of dye penetration. 0, no leakage; 1, superficial leakage (confined to the enamel only); 2, leakage to the DEJ; 3, leakage into dentine; 4, leakage to the pulpal wall of the preparation.
without burnishing or polishing the material. The amalgam restorations were also placed in 100 per cent humidity at 37°C for 36 h prior to thermocycling. Table I depicts the placement of samples in each experimental group, and Fig. I displays a cross-section diagram of a typical restoration with a glass ionomer liner. One-half of the samples from each restoration category were thermocycled in deionized water. with a temperature differential of46”C (4-50°C) for 625 cycles. Dwell time in each temperature bath was 30 s, with a transfer time of 10 s. After thermocycling, each specimen was coated to within 1.0 mm of the margin of the restoration with two applications of a toluene-based clear nail polish (Del Laboratories, Farmingdale, NY, USA). Only the crown of each specimen was immersed in a 0.5 per cent aqueous methylene blue dye solution (Ricca Chemical Co.. Arlington, TX. USA) for 6 h (Spangberg et al., 1989). After dye immersion, the teeth were rinsed with deionized water for 1 min and sectioned buccolingually through each restoration with a slow-speed diamond saw (Buehler, Ltd. Lake Bluff. IL. USA). Sectioned samples of the restorations were then examined at X 100 magnification with a light-diffraction microscope (Wild Photoautomat MPS 45) to determine the amount of dye penetration at the margins. Microleakage was visually scored according to the following scale: 0 = no leakage, 1 = superficial leakage (into the enamel only). 2 = leakage to the dentinoenamel junction. 3 = leakage into the dentine. and 4 = leakage to the pulpal wall (Fig. 2).
RESULTS The dye penetration scores for each treatment group are displayed in Table 1. The dental amalgam (Tytin) and glass ionomer restorative (Ketac-fil) restorations are
110
J. Dent. 1990;
18: No. 2
Table II. Significance U test (2P < 0.05)
of differences
in microleakage
scores
Variable
Comparison *
type type type type
using the Mann-Whitney
P value
TC-L-T NT-L-T TC- N L-T NT-N L-T
vs. vs. vs. vs.
TC-L-K NT-L-K TC-NL-K NT-NL-K
Restoration Restoration Restoration Restoration
T-L-TC T-N L-TC K- L-TC K-N L-TC
vs. vs. vs. vs.
T-L-NT T-N L-NT K-L-NT K-N L-NT
Thermocycling Thermocycling Thermocycling Thermocycling
0.0006 < 0.0001 0.0027 0.00 13
T-TC- L T-NT-L K-TC- L K-NT-L
vs. vs. vs. vs.
T-TC-N L T-NT-NL K-TC-N L K-NT-NL
Liner Liner Liner Liner
0.0002 0.0 104 0.00 13 < 0.0001
presence presence presence presence
0.0006 0.002 7 NS NS
*Comparison legend: T, dental amalgam (Tytin); K, glass ionomer restorative cement (Ketac-fil); TC, thermocycling; NT, no thermocycling; L, glass ionomer liner (Shofu); NL, noglass ionomer liner. NS, P value was not significant.
divided into glass ionomer-lined and unlined samples and further subdivided into thermocycled and nonthermocycled groups. Contingency tables were constructed from the data in Table Z and tested for statistical significance with x2 analysis, using 2P < 0.05 as the level of significance. For each leakage class, the scores of samples treated a specific way (e.g. thermocycled) were compared with the scores of the control samples (e.g. non-thermocycled). The MannWhitney U test was utilized to detect differences between individual treatment groups at the 2P < 0.05 level. TableZZ depicts the significance of differences in microleakage scores using this latter analysis. Significant differences in microleakage scores were found for each of the three treatment conditions: (1) type of restorative material (x2 = 103.44, d.f. = 19,2P < 0.0004), (2) thermocycling(x2 = 103.38, d.f. = 19,2P < 0.0004), and (3) presence or absence of the glass ionomer liner (x2 = 53.28, d.f. = 19, 2P < 0.0001). In addition, the Mann-Whitney U test indicated that microleakage around restorations that contained the glass ionomer lining cement was significantly different from that in samples in which no liner was placed (2P < 0.0001). Significant differences regarding restoration types were apparent when dental amalgam/lined/thermocycled samples ;were compared with the glass ionomer restored/ lined/thermocycled samples (2P < 0.0006); and also when dental amalgam/lined/non-thermocycled specimens were compared with the glass ionomer restored/lined/ non-thermocycled specimens (2P < 0.0027). Differences between unlined samples of dental amalgam (Tytin) and glass ionomer (Ketac-El) restorations, irrespective of thermocycling, were not found to be significant.
DISCUSSION The purpose of this study was to investigate the effects of glass ionomer liner placement in dental amalgam (Tytin)
vs. glass ionomer (Ketac-fil) restorations. In addition, the effect of thermocycling was evaluated to determine whether artificial ageing (thermocycling) caused significantly more microleakage with either restorative material or because of the presence of a glass ionomer liner. The use of methylene blue to detect marginal gaps between a tooth-restoration interface has been widely documented (Spangberg et al., 1989). The aqueous solution of methylene blue (0.5 per cent) allows for both the uptake of the dye within the matrix of the glass ionomer restoration and for penetration of the dye because of marginal deterioration. Dye tracers are much smaller than the 0.5 pm diameter that oral bacteria require to travel between the tooth-resin interface (Krell and Madison, 1985; Douglas, 1989). Therefore, the dye can be used as a stringent test of marginal microleakage. Previous research has demonstrated that the use of a glass ionomer liner was effective in reducing microleakage (Hinoura et al., 1987; Garcia-Godoy et al., 1988). Because of the tendency for operative restorations to exhibit microleakage, glass ionomer liners were proposed to lessen this potential for failure (McLean et al. 1985; Fayyad and Shortall, 1987). The results of this study also demonstrated that a glass ionomer liner reduced the occurrence of microleakage in amalgam restorations. In addition, a thermocycling model was utilized to ascertain the effects of accelerated ageing on the leakageinhibiting capacity of glass ionomer lining cements, irrespective of restoration type. The effect of thermocycling caused a significant difference in microleakage for all groups, when compared to the corresponding nonthermocycled controls. However, thermocycling did not cause the extreme effects associated with an ageing model perhaps because the duration of total cycling time (625 cycles) was not as long as in other studies (Lloyd et al., 1978; Davis et al., 1989; Arcoria et al., 1989). Alternatively, separate studies did indicate that short-term thermocycling could induce a significant amount of microleakage in
Arcoria et al.: Microleakage
composite resin and amalgam restorations (Yates et al., 1980; Gottlieb et& 1985: Crim and Shay, 1987; Schereret al., 1989). The presence of the glass ionomer liner was extremely important in reducing microleakage in either type of restorative material. If microleakage at the margins of restorations is a result of the lack of bond (seal) between the tooth substance and restorative material, then the microleakage should have been most apparent in the groups in which no liner was used. i.e. with direct physical contact between tooth substance and material. However, in this study. these differences were not statistically significant. Instead, the differences between restorative materials became significant only when a glass ionomer liner was interposed between tooth and restoration. This difference persisted in both the thermocycled and nonthermocycled groups. Whether this effect was due to the use of the type of liner chosen for this study or to the use of any type of liner needs further investigation. Glass ionomer cement bonds significantly less to dentine than to enamel (Coury et al., 1982). The difference in the inorganic composition of enamel vs. dentine accounts for this occurrence (higher proportion of calcium ions in enamel). As a result, the dentine bond to glass ionomer should be established before the enamel bond of the final restorative material is formed so as not to disturb the dentine-liner interface (Hinoura et al.. 1987). Understandably, the glass ionomer-lined composite restorations have demonstrated a detachment of the liner from the walls of the cavity preparation (Crim and Shay. 1987: Chan and Swift, 1989). The bond of composite resin to enamel is greater than the bond of the glass ionomer liner to dentine. Admittedly, a composite resin restoration will undergo polymerization shrinkage and/or imbibition of water (Bowen et al.. 1982) to a greater degree than a glass ionomer restorative material (Feilzer et al., 1988). However, glass ionomer cements also have the potential to exhibit shrinkage (although at a much slower rate than composite resins) and to absorb a great amount of water unless properly protected during the curing process. Consequently, the purpose of using a glass ionomer liner in this study was to wet the dentine with a material that acted as a primer for the final restoration. In addition, the liner was completely polymerized and bonded to the dentine before the glass ionomer restorative material was bonded to the liner and to the enamel. Although the glass ionomer restorative material (Ketac-fil) does not have a particularly high degree of viscosity, it adapted better to a preparation if a less viscous liner (Shofu) of similar composition acted as a primer for the final restoration. Observation of glass ionomer restorations devoid of a liner saw marginal gaps at the dentinoenamel junction with the dye penetrating to the deep portions of the preparation. This was particularly evident with the thermocycled samples. However, the non-thermocycled glass ionomer restorations without liners also displayed these marginal gaps at the dentino-enamel junction with resultant microleakage. This study demonstrated that the
with
glass-ionomer
liners
111
use of a glass ionomer liner in both dental amalgam and glass ionomer restorations was successful in reducing microleakage. Furthermore, the difference in microleakage between dental amalgam and glass ionomer restorations was significant only when a glass ionomer liner was present.
Acknowledgement This study was supported in part by Baylor Dentistry Research Funds.
College
of
References J. T. and Hembree J. H. (1980) Marginal leakage of amalgam alloys with high content of copper: a laboratory study. Oper. Dent. 5, 7-10. Arcoria C. J., DeWald J. P., Moody C. R. et al. (1988) Effects of thermocycling on amalgam and alloy-glass ionomer cores luted to cast gold crowns. Denr. Mater. 4, 155-157. Andrews
Arcoria C. J.. DeWald J. P.. Moody C. R. et al. (1989) A comparative study of amalgam and alloy-glass ionomer cores. J. Oral Rehabil. 16, 301-307. Bowen R. L., Rapson J. E. and Dickson G. (1982) Hardening shrinkage and hygroscopic expansion of composite resins. J. Dent Res. 61, 654-658. Brandau H. E., Ziermiecki T. L. and Charbeneau G. T. (1984) Restoration of cervical contours on non-prepared teeth using glass ionomer cement: a four and one-half year study. J. Am. Dent. Assoc. 108,782-783. Chan K. C. and Swift E. J. (1989) Leakage of chemical and light-cured basing materials. J. Prosthet. Dent. 62, 408-411. Coury T. L., Miranda F. J., Willer R. D. et al. (1982) Adhesiveness of glass ionomer cement to enamel and dentin: a laboratory study. Oper. Dent. 7,2-7. Crim G. A. and Garcia-Godoy F. (1987) Microleakage: the effect of storage and cyclic duration. J. Prosthet. Dent. 57, 574-576. Crim G. A. and Shay J. S. (1987) Microleakage pattern of a resin-veneered glass-ionomer cavity liner. J. Prosthet. Dent. 58, 273-276. Darbyshire P. A., Messer L. B. and Douglas W. H. (1988) Microleakage in class II composite restorations bonded to dentin using thermal and load cycling. 1 Dent. Res. 67, 585-587. Davis E. L., Joynt R. B., Wieczkowski G. et al. (1989) Bond durability between dentinal bonding agents and tooth structure. J. Prosthet. Dent. 62, 253-256. Douglas W. H. (1989) Clinical status of dentine bonding agents. J. Dent. 17,209-215. Fanian F., Hadavi F. and Asgar K. (1983) Marginal leakage of dental amalgam Oper. Dent. 8, l-7. Fayyad M. A and Shortall A. C. C. (1987) Microleakage of dentine-bonded posterior composite restorations. J. Dent. 15, 67-72. Feilzer A. J., DeGee A J. and Davidson (3. L. (1988) Curing contraction of composite restoratives and glass ionomer cements. J. Prosthet Dent. 59, 297-300. Garcia-Godoy F., Draheim R. N.. Titus H. W. et al. (1988) Microleakage of composite restorations with etched and non-etched glass ionomer bases. Am. J. Dent. 1, 159-162. Gottlieb E. W.. Retief D. H. and Bradley E. L. (1985) Microleakage of conventional and high-copper amalgam restorations. J. Prosthet. Dent 53, 355-361. Hinoura K.. Moore B. K. and Phillips R. W. (1987) Tensile bond strength between glass ionomer cements and composite resins. J. Am. Dent. Assoc. 114, 167-172.
112
J. Dent.
1990;
18: No. 2
Ibsen R., Ouellet D. and Strassler H. (1989) Clinically successful dentin and enamel bonding. Am. J. Dent. 2, 125-131. Knibbs P. J. (1987) A clinical report on the use of a glass ionomer cement to restore cervical margin lesions. J. Oral Rehabil. 14, 105-109. Krell K. V. and Madison S. (1985) Comparison of apical leakage in teeth obturated with a calcium phosphate cement or grossman’s cement using lateral condensation. J. Endodont. 11, 336-339. Lloyd B. A, McGinley M. B. and Brown W. S. (1978) Thermal stress in teeth. J. Dent Res. 51, 461-467. Maldonado A., Swartz M. L. and Phillips R. W. (1978) An in vitro study of certain properties of glass ionomer cement. J. Am. Dent. Assoc. 96, 785-791. Massler M. (1976) Oral problems in the aging patient. J. Indiana Dent. Assoc. 55, 13-15. McLean J. W. (1980) Aesthetics in restorative dentistry. Br. Dent. J. 149, 368-373. McLean J. W. (1984) Alternatives to amalgam alloys: I. Br. Dent. J. 157,432-433. McLean J. W., Prosser H. J. and Wilson A. D. (1985) The use of glass ionomer cements in bonding composite resins to dentin. Br. Dent J. 158,410-414. Mount G. J. and Makinson 0. F. (1978) Clinical characteristics of glass ionomer cement. Br. Dent. J. 145, 67-71.
Ngo H., Earl A. and Mount G. J. (1986) Glass ionomer cements: a 12-month evaluation. J. Pro&et. Dent. 55, 203-205. Olsen B. T., Garcia-Godoy F., Marshall T. D. et al. (1989) Fluoride release from glass ionomer-lined amalgam restorations. Am. J. Dent. 2, 89-91. Powis D. R., Folleras T., Merson S. A. et al. (1982) Improved adhesion of a glass ionomer cement to dentin and enamel. J. Dent. Res. 61, 1416-1422. Scherer W.. Kaim J., Lippman N. et al. (1989) Microleakage of three glass ionomer cement bases. Am. J. Dent. 2, 61-63. Spangberg L. S., Aciemo T. G. and Cha B. Y. (1989) Influence of entrapped air on the accuracy of leakage studies using dye penetration methods. J. Endodont. 15, 548-551. Swartz M. L.. Philips R. W. and Clark H. E. (1984) Long term fluoride release from glass ionomer cements. J. Dent. Res. 63, 158-160. Tjan A. H. and Morgan D. S. (1988) Metal-reinforced glass ionomers: their flexural and bond strength to tooth substrates. J. Pro&et. Dent. 59, 137-141. Welsh E. L. and Hembree J. H. (1985) Microleakage at the gingival wall with four class V anterior restorative materials. J. Prosthet. Dent. 54, 370-372. Yates J. L., Murray G. A. and Hembree J. H. (1980) Cavity varnishes applied over insulating bases: effect on microleakage. Oper. Dent. 5,43-46.
Book Reviews Diagnostic Picture Tests in Dentistry. P. J. Lamey and M. A. 0. Lewis. Pp. 128. 1988. Wolfe Medical. Softback, f 7.50. ‘An old soldier I perceive’ said Sherlock ‘and very recently discharged’, remarked ‘served in India, I see’ ‘and a non-commissioned Officer’ ‘Royal Artillery, I fancy’ said Sherlock. ‘And a widower’. ‘But with a child’ ‘children my dear boy, children’.
London,
the brother
Few dentists can match Holmes’ powers of observation and deduction and this little book should prove invaluable to them in preparing for the slide projection test of the FDS, or similar postgraduate, or even undergraduate, examinations. In 2 12, almost uniformly excellent clinical photographs, radiographs and photomicrographs, with questions and answers, Drs Lamey and Lewis provide an entertaining and informative quiz, successfully covering the major disciplines in general dentistry at just the right level. Equally, you can use it for a personal selfassessment, which certainly exposed the deficiencies in my own knowledge. Inspired guess-work is needed to identify the Paget’s disease depicted in figures 160 and 161 and only the nocturnal could decipher the murky radiograph in figure 8. In the next edition, an accompanying history and a better photomicrograph could be provided for the case of lichen planus shown in figure 51, but I suppose that minor injustices of this kind are, in themselves, all part of the average FDS examination. This book can be strongly recommended for such candidates, keen undergraduates and to any dentists feeling dangerously complacent about their general level of knowledge. D. M. Walker
A Guide to Dental Radiography, 3rd edition. Rita A. Mason. Pp. 226. 1988. Guildford, Butterworths. Softback, f 15.95. This third edition of A Guide to Dental Radiography has grown to 13 chapters and 226 pages. The book gives a complete description of all intraoral and extraoral techniques. For intraoral radiography paralleling, bisecting angle and occlusal film techniques are described in detail and the advantages of the ‘long cone’ technique stated. In addition to the chapters on extraoral techniques there are separate chapters describing radiography of the facial bones (including temporomandibular joint radiography), salivary glands and dental radiography for children. There is an extensive chapter on panoramic radiography describing the theoretical background to what the author terms ‘dental panoramic tomography’. Practical descriptions are given of how to operate panoramic machines and the effects of incorrect positioning of the patient are carefully illustrated. The chapters on radiation protection, factors affecting the radiograph, processing and image quality assurance all give the important background on how to diminish the damaging effects of X-rays but at the same time achieve a high quality radiograph. Different ways of keeping the dose to the patient as low as possible are emphasized within the description of each radiographic technique and there are many practical hints of use to the practitioner, in particular, some excellent summaries of advantages and disadvantages of the techniques described. The book is easy to read and the illustrations are carefully selected and reproduced to a very high quality. The guide is especially useful to the dental practitioner, but can also be highly recommended as a textbook for students of dental radiography. A. Petersson
