Background Osteotome sinus floor elevation (OSFE) is used to increase the bone volume at the site of the maxillary sinus through the transalveolar approach. However, there is uncertainty regarding the necessity of the use of grafting material in order to maintain the space for new bone formation. Objective This study aimed to evaluate new bone formation 6 months after osteotome sinus floor elevation without grafting and to evaluate the correlations between residual bone height (RBH), implant protrusion length (IPL), and endo-sinus bone gain (ESBG). Material and methods Thirty-one implants (27 patients) from area 14–17 and 24–27 were included in the study. All implants had a history of OSFE without grafting, with cone beam computed tomography (CBCT) taken prior to the surgery. The clinical examination and radiographic examination using CBCT were performed again 6 months after implantation. The RBH, new bone level, ESBG, and IPL were measured. Paired sample t test and Pearson correlation were used to analyze the data. Results The average RBH before surgery was 7.14 ± 1.07 mm and 6 months after surgery was 8.95 ± 1.17 mm. There was a significant increase in new bone formation in the 6 months following surgery ( p < 0.05). The average ESBG and IPL were 1.8 ± 0.79 mm and 2.02 ± 0.73 mm, respectively. There was a significant positive correlation between the IPL and ESBG ( p < 0.05) while there was a negative correlation between RBH and ESBG. This study also demonstrates a decrease in the percentage of bone formation in relation to IPL as the IPL increases. The survival rate of the implant was 100%. Conclusion Significant new bone formation can be detected around the implant site 6 months after implantation using OSFE technique without grafting. There is a negative correlation between the RBH and ESBG. While IPL is correlated to ESBG and appears to be the influencing factors of bone formation changes in the maxillary sinus. The preliminary radiographic results suggest that OSFE technique without grafting in combination with optimal IPL can provide sufficient bone height for implant support with a 100% implant survival rate. Electronic supplementary material The online version of this article (10.1186/s40729-019-0181-7) contains supplementary material, which is available to authorized users.