A Survey of the Composite Curing Units Used in the Dental Institutions of Karachi, Pakistan

A Survey of the Composite Curing Units Used in the Dental Institutions of Karachi, Pakistan
Farhan Raza Khan1, Ashar Jamille, Fahad Umer3, Syed Sheeraz Hussain4

How to CITE:

J PakDentAssoc. 2011 (4) : 222-225


To evaluate the light intensity output of the composite curing units used in the dental institutions of Karachi.


It was a cross sectional study in which a total of 29 halogen composite curing units were examined. The light intensity output was measured using Cure-Rite meter. A cut off of 300mW/cm was taken as adequate light output.ANOVAandKruskal-Wallis testwere applied.Level of significancewas kept at 0.05.


The mean light output intensity was 345.2 mW/cm (SD 251.1 mW/cm ). Out of 18 units at undergraduate institutions, 11 had poor light output while 3 out of 11 at postgraduate institutions had poor light output.The condition of light cure unit’s casing had a significant associationwith the light output (p-value of 0.011).


About half of the curing units at the dental institutions have poor light intensity output which may result in an inadequate quality of dental service.This is an alarming situation for the clinicians.Asmishandling of the equipment is a leading cause of its poor performance, the external casing of the light cure unit can be taken as a proxy for its light output.


CompositeRestorations,CuringLight,Light intensity,Dental Institutions


he composite light curing units have been used in dentistry for over three decades. The majority of these units are based on quartz-tungsten-halogen (QTH) lamps that emit light within the wavelength range of 400 to 500 nanometers. When curing light is exposed to composite restorative material, it passes through it and during which it is absorbed and scattered; as a result, its intensity decreases. This may cause the deeper layers of the material to polymerize insufficiently, resulting in inferior physical and mechanical properties of the restoration.

Factors that may affect polymerization of composite restorations include light intensity, exposure time, wavelength as related to the type of photo initiator incorporated in the composite material, thickness of the composite increment, distance between light guide tip and surface of the composite, shade of the composite and composition of the compositematerial. Of all these factors, light intensity seems to be themost important.

The light intensity can be influenced by factors such as years of clinical service of curing unit, breakage in fiber optic bundles of light guide tip, voltage, aging of bulb, deterioration of wavelength band filter or debris adherent to light guide tip may affect the light output intensity of the composite curing unit. Although, there is no acceptable single minimum value of intensity that has been validated scientifically, intensity of less than 300 milliwatts per square centimeter is usually considered as inadequate.

Inadequate light intensity can be an important quality issue, as itmay result in insufficient polymerization of the restorative material resulting in postoperative sensitivity in the restored tooth. Since, there is no study on the performance of composite curing units in Pakistan; our study can alert the dentists about the performance of curing units for optimal polymerization of composite materials.We hypothesized that the light intensity output of the composite curing units used in Operative Dentistry Departments of undergraduate and postgraduate dental institutions inKarachi is inadequate.


It was a Cross sectional study conducted at the Operative Dentistry clinics of the following institutions during: A- Postgraduate Institutions: Aga Khan University Hospital, Liaquat National Hospital, Alvi Dental Hospital, Abbasi Shaheed Hospital, Jinnah PostgraduateMedicalCenter B- Undergraduate Institutions: Karachi Medical & Dental College, Baqai Dental College, Fatima Jinnah Dental College, Jinnah Medical & Dental College, Liaquat Memorial College of Dentistry, Hamdard University Dental College, Altamash Ins ti tute of Dental Medicine, Zi auddin UniversityDentalCollege.

Inclusion criteria:

All Quartz-tungsten-halogen (QTH) resin curing units installed at dental institutions of Karachi.

Exclusion criteria:

Plasma arc (PAC) units, Light emitting diode (LED) units and laser curing unitswere excluded.Non functional units or curing units that are not in routine use were excluded.

Data collection procedure:

Initially permission was obtained fromthe principals or faculty of the institutions to physically visit and conduct the survey. Physical examinations of the units were done at time thatwas convenient for the hosts, usually at the end of a clinical session. In the second phase, inspection of each light curing unit was done. Inspection included examination of the fiber-optic light guide tip for damage (cracks, crazing and chipping) and adherent debris; and assessment of the condition of the electrical lead and outer casing.


he light output intensity was measured by the light intensity meter (Caulk Cure-Rite by L.D. Caulk / Dentsply,Milford, DE, USA) as shown in the annexure I. The light unitwas activated for 10 seconds, the light guide tip placed over the light sensor for a further 10 seconds, and the digital readout was noted at the end of the time period. Three readings at least 1 minute apart were taken and the average digital readoutwas recorded for each light unit.

To monitor the performance of survey meter, a light cure unit (Polylux, Kavo, Germany) at principal investigator’s institutionwas used as a control.

Data collection tool:

The proforma used in data collection is attached as annexure II.


SPSS 15.0 for Windows was used for statistical analysis. Means and standard deviation of quantitative variables and frequency of all the variables were determined. The association between the mean intensity reading (outcome variable) and the variables like age of the bulb, condition of light guide tip, guide tip diameter, repairs and other categorical variables were determined with the help ofANOVA, and Kruskal-Wallis test at 0.05 level of significance.


There were 29 light curing units installed in the 13 institutions of Karachi. The recorded range of light output was from 0 to 777.6 mW/cm . The mean value was 345.2 mW/cm and SD251.1mW/cm Therewere 18 units in the postgraduate and 11 in undergraduate institutions. The mean output of curing light in undergraduate was 300.5 mW/cm with SD 229.8 mW/cm while at post graduate institutions, it was 418.4 mW/cm with SD 277.9. The difference was not statistically significant (p value= 0.253) as shown in Table I.

Independent samples t test was applied at 0.05 level of significance.

A wide variety of light cure units belonging to a various manufacturers were observed during the study as illustrated in table II. Out of 18 units installed at undergraduate institutions, 11 had poor light output (cut off was 300 mW/cm or less) while 3 units (out of 11) at postgraduate institutions had poor light output as shown in Figure 1.

We found no association between light output intensity and variables like period of service, repairs of unit, diameter of light guide tip, adherent debris. The only significant association was observed in the condition of light cure unit’s casing which had a p-value of 0.011. (Table III).

All units were used by multiple operators and no under graduate institution had curing light meter in their department.


We observed that about half (14 out of 29) curing units in dental institutions of Karachi had an unacceptable light intensity (less than 300mW/cm ).This is an alarming situation for dentists. The restorations placed using such

curing units would not serve any benefit to the patients. The restorations will have poor physical strength, increased chances of micro leakage, post operative sensitivity and secondary caries. Thus, these limited longevity restoration would definitely create iatrogenic problems for the patients. As most of the teaching institutions in Karachi are run by private sector where patients pay directly from their pockets, the provision of inferior quality restorations service would definitely bear cost implications to the patients.

But this poor quality light output issue is not confined to developing countries. Studies from Texas ,Australia , Tokyo , Israel and Canada have reported somewhat similar situation. These studies have noticed a wide range of light intensities and concluded that light intensities used in some practices were lower than what is needed for optimum polymerization of composite restorations.

Four international studies reported that 12 – 55% of the lights in dental offices had intensity values less than 300 mW/cm . An Indian study showed that 18% percent of the curing lights had intensities of less than 200 and 71% lights had their intensities in the range of 200 to 400mW/cm2, respectively. The scenario in Karachi is no different, our study showed 48.3% curing units had intensity below 300mW/cm

We observed that, a large proportion of the low output curing units was installed at undergraduate institution and this inadequate output was associated with poor condition of the casing. We can speculate that most likely cause is the mishandling of the equipment by the operators. In this case, the operators are the students, house officers and clinical staff at these institutions.

We did not found any association of low output of light with factors such as ageing of light bulb or curing tip diameter. But hedge & colleagues reported that aging of bulb over 36months did decrease the light output in curing units. The major limitations of our study is that it were a snap shot assessment of condition of curing units, limited sample size and uncertain information about the service life of equipments. However, with these limitations, we stillmanaged to achieve the study’s objective.


About half of the curing units at the dental institutions of Karachi have poor intensity output which result in an inadequate quality of dental service. This is an alarming situation for the clinicians who offer composite restorations. As mishandling of the equipment is a leading cause of poor performance of curing unit, the external appearance of the light cure unit can be taken as a proxy for its output


All dental teaching institutions should ensure periodic inspections of composite curing units tomaintain the service quality. Continuous monitoring would improve the situation.

Conflict of Interest:

Therewere no conflicts of interest involved.

Sources of Funding Statement:

The study was sponsored by the Aga Khan University, ref: URC: 06GS020SUR and was approved from the Ethical review committee of the same institution, ref:ERC: 641-Sur/ERC-06.9


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