Clinical evaluation and quantitative occlusal change analysis of posterior implant-supported all-ceramic crowns: A 3-year randomized controlled clinical trial

OBJECTIVES

To compare the survival and complication rates of posterior screw-retained monolithic lithium disilicate (LS2 )/veneered zirconia (ZrO2 ) single implant crowns (SICs), as well as analyze the occlusal changes observed during a 3-year follow-up period.

MATERIALS AND METHODS

Thirty-three patients were included and randomly divided into two groups. The test group consisted of 17 patients who received monolithic-LS2 -SIC, while the control group consisted of 16 patients who received veneered-ZrO2 -SIC. Implant/prosthesis survival rates, technical complications, peri-implant soft tissue conditions, and quantitative occlusal changes of SIC (obtained by the intra-oral scanner and analyzed in reverse software Geomagic Control 2015) were assessed at 1- and 3-year follow-ups. Bone loss and Functional Implant Prosthodontic Score (FIPS) were evaluated at a 3-year follow-up.

RESULTS

After a 3-year follow-up period, one patient dropped out of the follow-up. No implant loss was observed. One crown was fractured, resulting in prosthesis survival rates of 93.75% for the monolithic group and 100% for the veneered group. A technical complication rate of 25% (4/16) was observed in the veneered group (p = .333). No significant differences in the marginal bone loss were observed at the 3-year follow-up (0.00 (-0.22, 0.17) mm versus 0.00 (-0.12, 0.12) mm, p = .956). The total FIPS scores for the test group were 9.0 (9.0, 9.0), while the control group received scores of 9.0 (8.0, 10.0) (p = .953). The changes in mean occlusal clearance were 0.022 ± 0.083 mm for the test and 0.034 ± 0.077 mm for the control group (at 3 years, p = .497). The changes in occlusal contact area were 1.075 ± 2.575 mm2 for the test and 1.676 ± 2.551 mm2 for the control group (at 3 years, p = .873).

CONCLUSION

After a 3-year follow-up, screw-retained monolithic LS2 and veneered ZrO2 SIC demonstrated similar survival rates. The occlusal performance of implant prostheses needs to be closely examined during follow-up, and appropriate occlusal adjustments need to be considered.

Adjunctive controlled intrusion of the maxillary first molar using orthodontic miniscrews

In the absence of the mandibular first molar, there is corresponding supra-eruption of the maxillary first molar, which can lead to occlusal interferences compromising the space available for restoration with a prosthesis. In this case report, the maxillary left first molar intrusion has been discussed with the use of two miniscrews. A 28-year-old female reported with a missing mandibular left first molar and wanting to replace it with a dental implant. The patient presented with a Class I skeletal relation, mild proclination of the anteriors and occlusal contacts. The maxillary first molar had erupted by >4 mm beyond the occlusal plane, thereby reducing the space available for placement of a lower prosthetic crown. After 5 months of intrusion, the desired occlusal clearance was achieved, and impressions were recorded. For retention, the patient was given an upper clear vacuum retainer and the crown was placed on the implant.

Nonsyphilitic occurrence of mulberry molars: A rare case report

Developmental defects of enamel may range from slight abnormalities of the tooth's color, shape and size to a complete absence of the enamel. Permanent first molar may show large variations in their morphological features and forms. Such changes may be in the form of anomalous cusps or variations in the occlusal surface showing globular shaped additional cusps and also increased in number of roots. However, to the best of our knowledge, this is the first nonsyphilitic case with the occurrence of multiple globular cusps. In the present case, occlusal anatomy is abnormal, with numerous disorganized globular projections involving all four permanent first molars. The projections of 2 mm × 2 mm in size and globular in shape were seen in the maxillary and mandibular cast. The features resemble the surface of mulberry and hence diagnosed as mulberry molars.

An ectodermal dysplasia patient treated with a small diameter implant supporting a single crown

Ectodermal dysplasia (EDD) is a developmental disorder that affects the skin, hair, and teeth among other organs generated in the ectoderm. Dental implants have been used to successfully treat partial edentulism in EDD patients, but the success rate is much lower for these patients. The report herein is a successful case of a single mini, small diameter, implant used to support a single crown of a mandibular right second premolar. A review of implant treatment in EDD patients is included.

Analysis of masticatory muscle coordination during unilateral single-tooth clenching using muscle functional magnetic resonance imaging

In a previous study, we used muscle functional magnetic resonance imaging to show that the anterior movement of the occlusal point increased the activity of the superior head of the ipsilateral lateral pterygoid muscle (ipsilateral SHLP) during unilateral single-tooth clenching. The purpose of this study was to verify the hypothesis that the increased activity of the ipsilateral SHLP described above serves to antagonise the occlusal force acting on the condyle. In total, 9 healthy volunteers were requested to perform left unilateral clenching at the first molar or first premolar region for 1 minute at 20% or 40% maximum voluntary clenching force. Changes in the mean proton transverse relaxation time (∆T2) were examined from the magnetic resonance images obtained before and after each clenching act as an index of the activity in all masticatory muscles. Correlation analyses of the mean ΔT2 for each volume of interest were performed with the first molar or premolar clenches to analyse the correlation between the activities in each muscle. A statistically significant correlation was exhibited between the ipsilateral temporal and ipsilateral SHLP (r = .651, P = .003) during first premolar clenching. However, no significant correlations were observed in the ipsilateral SHLP during first molar clenching. The results of this study suggest that the ipsilateral SHLP may contribute to the pulling of the mandibular condyle forward against the occlusal force generated by the ipsilateral temporal muscle.

Association between brain lateralization and mixing ability of chewing side

Background/purpose

Previous studies have suggested that functional dominance in one part of the body can be correlated with functional dominance in another part. Thus, the present research aimed to determine whether brain laterality (handedness, footedness, earedness, and eyedness) was related to mixing ability and chewing side preference.

Materials and methods

Fifty-four volunteers who were not undergoing any form of dental treatment took part in this study. Self-defined brain laterality was determined through a questionnaire. The volunteers performed five tasks related to brain laterality, which was identified by the side used to perform three or more of the five tasks. Chewing side preference was determined by observing the main gum location on the occlusal area when volunteers chewed for 30 strokes. Mixing Ability Index (MAI) was measured by analyzing the degree of mixing of two differently colored waxes (height, 3 mm; diameter, 20 mm). Occlusion contact area was measured by taking the maximum intercuspation bite with polysiloxane.

Results

Thirty-nine volunteers (72%) showed significant agreement between brain dominance and chewing preference side. The association between brain dominance and MAI was not significant. The occlusal contact area of the dominant side (mean = 48.2 mm²) was significantly wider than that of the nondominant side (25.7 mm²).

Conclusion

Brain laterality can be explained by the side of functional (preference of the hands, eyes, ears, and feet, and survey) has a positive correlation with chewing preference side. MAI between the brain dominant and nondominant sides was not significant. This shows that mastication efficiency does not differ between dominant and nondominant sides. So, this study suggests that brain dominance is correlated with chewing preference, but it does not affect efficiency of mastication.

Evaluation of masticatory activity during unilateral single tooth clenching using muscle functional magnetic resonance imaging

Masticatory muscle activity during teeth clenching is affected by occlusal pattern. However, few studies have performed simultaneous evaluation of all masticatory activities during teeth clenching under various occlusal conditions. The aim of this study was to use muscle functional magnetic resonance imaging (mfMRI) to evaluate the effects of changes in occlusal point on masticatory activity during single tooth clenching. Changes in mean proton transverse relaxation time (∆T2) as an index of activity in all masticatory muscles during left unilateral clenching at the first molar or first premolar for 1 min were examined in nine healthy volunteers. Bite force was maintained at 40% of the maximum voluntary clenching force. The ∆T2 values of the masseter and lateral pterygoid muscles were analysed separately for superficial and deep layers, and for superior and inferior heads. The ∆T2 values for the ipsilateral deep masseter were significantly lower, and for the superior head of the ipsilateral lateral pterygoid muscles were significantly higher, after left first premolar clenching compared to left first molar clenching. These results quantitatively demonstrate a significant increase in activity of the superior head of the ipsilateral lateral pterygoid muscle and a significant decrease in activity of the ipsilateral deep masseter muscle with forward displacement of the occlusal contact point during unilateral tooth clenching.

A data-based study on survival of permanent molar restorations in adolescents

OBJECTIVE

The aim of this epidemiological, data-based survival study was to study the longevity of restorations in permanent molars of adolescents in the 1990 and 1995 birth cohorts during the period of 1992-2005 in the City of Vantaa, Finland.

MATERIALS AND METHODS

The dental records of 2975 (1990 cohort) and 3147 (the 1995 cohort) adolescents were analyzed. The longevity of restorations from their placement until replacement was illustrated using the Kaplan-Meier survival curves. The influence of the cohort, gender and caries risk on the survival rate was assessed using the Cox proportional hazards regression analysis.

RESULTS

A majority of the restorations were tooth-colored. The proportion of amalgam restorations was almost non-existent in both cohorts. The survival of tooth-colored restorations on the occlusal surfaces of molars was lower in the 1995 cohort compared to the 1990 cohort. The need of replacement of glass-ionomer restorations was twice that of composite restorations' hazard ratio 2.27 (1.62-3.16).

CONCLUSIONS

Composites are the most frequently used dental materials and have the longest survival times among adolescents. The survival of restorations per se is poorer in the more recent than in the earlier birth cohort.

The total occlusal convergence of the abutment of a partial fixed dental prosthesis: A definition and a clinical technique for its assessment

The abutment(s) of a partial fixed dental prosthesis (PFDP) should have a minimal total occlusal convergence (TOC), also called a taper, in order to ensure adequate retention of a PFDP that will be made for the abutment(s), given the height of the abutment(s). This article reviews the concept of PFDP abutment TOC and presents an alternative definition of what TOC is, defining it as the extent to which the shape of an abutment differs from an ideal cylinder shape of an abutment. This article also reviews experimental results concerning what is the ideal TOC in degrees and explores clinical techniques of estimating the TOC of a crown abutment. The author suggests that Dentists use high magnification loupes (×6-8 magnification or greater) or a surgical operating microscope when preparing crown abutments, to facilitate creating a minimum abutment TOC.

Pattern of dental caries in Mulago Dental School clinic, Uganda

Information on dental caries among patients attending Mulago Hospital is scarce. Yet knowledge of the pattern of caries can be used to plan preventive and treatment interventions. This study describes the pattern of dental caries (in terms of age group, tooth and tooth surface and gender) among patients attending the Public Health Dental Officers School Clinic, Mulago Hospital.

METHODOLOGY

A review of patients' treatment records for the period 1995 to 1999 was done. A total of 1800 cards were reviewed for the diagnosis of dental caries, age, gender and the data was analyzed using EPI INFO 6 program. The patients were from both urban and peri-urban settings and were aged between 10-90 years.

RESULTS

The results showed that the most frequently affected tooth surface was the occlusal (68.8%) followed by the interproximal (24%) and the least affected was the lingual/palatal (1.5%). The second molars were found to be the most affected of all teeth, with tooth 37(12%), 47(11%), 17(9.5%) and 27 (9.1%). The distribution of caries was higher in the lower than the upper jaw. There was a slight difference in sex predilection with females having 54.5% and males 45.5% of the lesions and the age group most affected was 20-29 years.

CONCLUSION

The results showed a high occurrence of occlusal surface caries in molars especially the second molars in the 20-29 age group in the patients attending the Public Health Dental Officers School Clinic, Mulago Hospital.